(CNN) — Syrian President Bashar al-Assad should heed U.S. warnings to neither use nor move chemical or biological weapons, lest he risk crossing a “red line” and provoke a U.S. military response, President Barack Obama said Monday.
“We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people,” Obama told reporters at the White House. “We have been very clear to the Assad regime — but also to other players on the ground — that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized.
“That would change my calculus; that would change my equation.”
Obama added that U.S. officials are monitoring the situation “very carefully” and have put together a number of contingency plans.
Members of the Free Syrian Army prepare their weapons in Aleppo’s Saif al-Dawla district on Monday, August 20.
Syrian bakers work in the northern city of Aleppo on Sunday, August 19, the first day of Eid al-Fitr, marking the end of the holy fasting month of Ramadan.
In this image provided by Syria’s national news agency, SANA, President Bashar al-Assad, center, is greeted by a cleric while attending Eid al-Fitr prayers at al-Hamad mosque in Damascus on Sunday, August 19.
Members of the Free Syrian Army and residents try to extinguish a fire that they say was caused by shelling by forces loyal to al-Assad in the Damascus suburb of Saqba on Friday, August 17.
A Free Syrian Army fighter takes aim during clashes in Aleppo on Friday, August 17. For days, the northern Syrian city has been at the center of some of the worst fighting in the 18-month-old conflict.
A rebel fighter makes his way through a hole in a wall during fighting Friday in Aleppo, Syria’s largest city.
A rebel climbs some stairs in a building during clashes in central Aleppo’s Salaheddine neighborhood.
A rebel fighter runs for cover as a Syrian army tank shell hits a nearby building Friday in Aleppo. The opposition accuses Syrian forces of shelling flashpoint neighborhoods in Aleppo where rebels are making a stand.
Free Syrian Army fighters dress a mannequin to look like a fighter to draw gunfire away from them Friday in Aleppo.
Free Syrian Army fighters rest Friday in Aleppo during a lull in fighting.
A fighter with the rebel Free Syrian Army secures a street Friday in the Damascus suburb of Saqba. Fighting raged unabated Friday across Syria, while diplomats struggled to find a political solution.
Members of the Free Syrian Army try to secure a street Friday in Saqba.
The Free Syrian Army takes charge of a street in Saqba.
A rebel holds a rocket-propelled grenade Friday in the Damascus suburb.
A Free Syrian Army fighter fires an anti-aircraft gun at a Syrian air force helicopter in Aleppo on Thursday, August 16.
Free Syrian Army fighters carry the body of a fellow fighter during clashes Thursday in Aleppo. Government forces are pounding Syria’s largest city in a siege that’s become the focal point of the civil war.
A grief-stricken woman clutches her dead baby while her husband’s body is covered up following a regime airstrike on Azaz, a town near Aleppo, on Wednesday, August 15.
Syrians search for people trapped under the rubble after the airstrike Wednesday in Azaz, near Aleppo.
A man removes his belongings from his destroyed car at the airstrike site.
A Free Syrian Army fighter fires an AK-47 rifle in Aleppo on Wednesday, August 15.
Syrians carry the body of a woman after an airstrike in Azaaz.
A Syrian man reacts after an airstrike in Azaaz.
Syrians flee Azaaz following the airstrike.
A Syrian youth holds the arm of someone trapped under rubble after an airstrike in the town of Azaaz, on the outskirts of Aleppo.
Black smoke billows into the air after a bomb exploded at a military site car park near a hotel used by United Nations monitors in Damascus. The explosion Wedesday wounded three people, Syrian state television said.
Firefighters work at the scene of a bomb explosion in central Damascus. The bomb was planted under a diesel tanker.
A man carries the body of a boy after a Syrian Air Force strike on Azaz, some 29 miles north of Aleppo.
A man sits in front of tombstone workshop in Aleppo.
Jordanian security guards patrol the entrance of the Zaatari refugee camp, located outside the northern Mafraq, Jordan, which borders Syria. Refugees face the hardships of sweltering heat, dust, lack of electricity and at times sexual harassment in this UN-run desert tent camp.
Jordanian security officers detain a Syrian man after he tried to escape from the Zaatari refugee camp in Mafraq.
A Free Syrian Army fighter learns that his commander has been killed by a tank shell in Aleppo on Tuesday, August 14. Opposition activists say shelling in dissident strongholds has exacerbated the humanitarian crisis in the country.
Free Syrian Army fighters look at the body of their commander killed by a tank shell Tuesday in Aleppo.
A Free Syrian Army fighter fires his rifle in Aleppo on Tuesday.
Syrian rebels fire toward a sniper in Aleppo on Monday, August 13, as fighting continues against Syrian government forces.
A rebel fighter fires at government forces Monday in Aleppo’s Salaheddin neighborhood.
A Syrian rebel climbs a staircase in Aleppo’s Salaheddin district as the opposition battles the regime.
A man gives bags of bread to customers at a bakery run by the opposition Free Syrian Army in Aleppo, Syria’s largest city.
Rebels covered in dust and debris emerge from a building hit by an army tank shell Monday in Aleppo’s Salaheddin area.
A rebel fighter gestures toward others after emerging from a shelled building during fighting Monday with government forces.
A Free Syrian Army sniper looks through the sight on his rifle from a house in Aleppo on Monday.
Rebel fighters sit behind a barricade of rocks on an Aleppo street.
Free Syrian Army fighters walk down a debris-covered street Monday in central Aleppo’s Salaheddine neighborhood.
A Free Syrian Army fighter fires an RPG as a Syrian army tank shell hits a building across a street during heavy fighting in central Aleppo on Saturday, August 11.
A Free Syrian Army fighter sits on a window sill as he holds an AK-47 rifle in central Aleppo.
A Free Syrian Army fighter aims his rifle during heavy fighting in the Salaheddine neighborhood.
A Free Syrian Army fighter fires an RPG after a Syrian army tank shell hit a building during heavy fighting in the Salaheddine neighborhood.
A Free Syrian Army fighter tries to fix his jammed rifle during heavy fighting in the Salaheddine neighborhood.
A Free Syrian Army fighter runs for cover during heavy fighting in the Salaheddine neighborhood.
Free Syrian Army fighters walk through a damaged building during heavy fighting in the Salaheddine neighborhood.
A Free Syrian Army fighter aims an RPG as he waits for Syrian army tanks in the Salaheddine neighborhood.
A Free Syrian Army fighter walks on an empty street in the Salaheddine neighborhood.
Free Syrian Army members check a confiscated cache of weapons found on a truck that was searched at a checkpoint in Dana.
A rebel fighter fires an anti-aircraft gun during a regime airstrike on Tel Rafat, a village north of Aleppo, on Thursday, August 9. The Syrian government and rebel groups have been battling for control of Aleppo, a key front in the conflict that has morphed into a civil war.
A Syrian air force fighter plane fires during an airstrike Thursday in Tel Rafat, north of Aleppo. Forces loyal to the regime have been shelling Aleppo, Syria’s largest city.
A truck burns after apparently being hit by rockets during an airstrike on Tel Rafat.
Men carry the body of a boy killed in an airstrike in the village of Tel Rafat.
A boy’s body is uncovered in the rubble of a house demolished during the recent clashes in Tel Rafat.
A man steps on a carpeted image of Syrian President Bashar al-Assad in Anadan, northwest of Aleppo, on Wednesday, August 8. The fighting has taken a toll on al-Assad’s regime, which has been hit by assassinations and political and military defections.
Residents sift through rubble Wednesday searching for bodies under a collapsed house destroyed in an airstrike.
Syrian refugees bathe Wednesday at Al Zaatri U.N. camp in the Mafraq, Jordan, near the border with Syria. The recent shelling has led thousands of residents to flee Syria.
Syrian refugees cook a meal at Al Zaatari camp in Mafraq, Jordan.
A Syrian rebel prepares his weapon as a group of Free Syrian Army fighters head toward the fighting with Syrian Army soldiers in the Salah ad-Din neighborhood of central Aleppo on Sunday, August 5.
Syrians evacuate a civilian wounded in shelling in the northern city of Aleppo on Saturday, August 4. Syria’s armed forces pounded Aleppo’s rebel-held Salah ad-Din district with air and ground fire as violence also raged in the Shaar and Sukkari districts, according to reporters in the area and a rebel commander.
A vehicle burns as Syrians walk through debris from clashes between Syrian armed forces and rebels in the northern city of Aleppo on Saturday, August 4.
A boy plays on the gun of a destroyed Syrian army tank partially covered in the rubble of the destroyed Azaz mosques, north of the restive city of Aleppo, on Thursday, August 2.
Smoke rises from Al-Safsaf in Homs on Friday, August 3.
A boy plays with an AK-47 rifle owned by his father in Azaz, some 29 miles north of Aleppo on Friday, August 3.
Syrians climb on an abandoned Syrian army tank north of Aleppo on Thursday, August 2.
A man looks at a destroyed Syrian army compound in Azaz, 29 miles north of Aleppo on Friday, August 3.
A Syrian refugee walks at the Al Zaatri refugee camp in the Jordanian city of Mafraq, near the border with Syria, on Friday, August 3.
People and a member of the Free Syrian Army commute on Wednesday, August 1, past a building on the outskirts of Idlib that was hit by rocket fire Tuesday night by forces loyal to President Bashar al-Assad. Unrest spread across other volatile regions of the country as al-Assad’s forces shelled targets and launched raids in and around Damascus, Homs, Daraa and Deir Ezzor.
A woman and child on Wednesday walk through rubble of a building destroyed by shelling from forces loyal to Syrian President Bashar al-Assad in Aleppo.
Demonstrators hold an opposition flag during a protest Wednesday against Syria’s President Bashar al-Assad in Damascus.
Syrian girls on Wednesday walk past a Syrian army tank captured two days earlier by rebel fighters at a checkpoint in the village of Anadan. The strategic checkpoint secures the rebel fighters free movement between the northern city of Aleppo and Turkey.
Rebel Free Syrian Army fighters capture a policeman who they allege is a “Shabiha” or pro-regime militiaman, on Tuesday, July 31, as the rebels overrun a police station in Aleppo.
Rebel fighters load an anti-aircraft machine gun on an armored vehicle in Atareb, east of Syria’s second-largest city, Aleppo, on Tuesday, July 31.
Syrian boys run near a building hit by bullets and fire in Atareb.
A member of the Free Syrian Army fires at forces loyal to President Bashar Al-Assad in a district of Aleppo called Salah Edinne on Tuesday.
A member of the Free Syrian Army carries an injured civilian to safety in Aleppo’s district of Salah Edinne on Tuesday.
Members of the Free Syrian Army learn that a tank belonging to forces loyal to President Bashar Al-Assad is heading to the area.
A Syrian boy carries bags of bread as people wait outside a bakery near Syria’s second-largest city, Aleppo.
A photo released by Syrian Arab News Agency depicts damaged buildings in Homs on Monday, July 30.
A Free Syrian Army fighter takes position Sunday, July 29, in Aleppo as people flee shelling. Intense clashes have been under way for more than a week between the regime and rebels in Aleppo, Syria’s commercial and cultural center.
Parts of Syria’s largest city saw the fiercest clashes yet in the country’s 16-month crisis on Saturday, July 28. About 200,000 people have fled fighting in Aleppo and surrounding areas in the past two days, a U.N. official says.
Fighting leaves vehicles damaged Saturday in the southwestern city of Daraa.
Syrians carry the body of a man allegedly killed in the bombardment of Sukari, southwest of Aleppo, by Syrian regime forces on July 27.
Destruction appears widespread in Homs on Friday, July 27, in a handout photo from the Syrian opposition Shaam News Network.
A Syrian opposition fighter takes aim during clashes with forces loyal to President Bashar al-Assad in Aleppo on Wednesday, July 25.
Family and friends mourn over the body of Usame Mircan, who they say was killed by a Syrian government sniper in Aleppo on Wednesday.
Usame Mircan’s mother grieves after he was killed during fighting in Aleppo.
The bodies of men killed during clashes between Syrian rebel fighters and goverment forces lie on the Aleppo street on Thursday, July 26.
Fighters from the Syrian opposition rest at a former primary school in Aleppo on Wednesday.
Residents take cover as fighters from the Syrian opposition clash with forces loyal to President Bashar al-Assad in Aleppo on Wednesday.
Syrian rebels guard a checkpoint in Aleppo on Wednesday.
A damaged portrait of President Bashar al-Assad sits among piles of debris at a checkpoint manned by Syrian rebels in Aleppo on Wednesday.
Syrian rebels drive through Selehattin near Aleppo during clashes with government forces on Monday, July 23.
A Syrian rebel runs through the streets of Selehattin during an attack on a municipal building. The rebel Free Syrian Army says it is attempting to “liberate” several districts of Aleppo.
Syrian rebels work to find snipers during clashes Monday between the opposition and government forces in Selehattin.
Syrian rebels make their way down a street Monday in Selehattin near Aleppo. If they gain control of Aleppo, it would mark a pivotal point in the Syrian crisis.
Syrian rebels take cover behind sandbags during fighting Monday at the entrance to the city of Selehattin.
On Sunday, July 22, a Syrian refugee looks out from a bus as he arrives at a refugee camp in Turkey opposite the Syrian commercial crossing point Bab al-Hawa.
Syrian refugees flee from a refugee camp nicknamed “Container City” on the Turkish-Syrian border in Kilis province, southern Turkey, on Sunday.
A mortar shell falls toward the Syrian village of Jbatha Al-khashab, about 45 kilometers (28 miles) south of Damascus. It’s seen from the Israeli side of the border, in the Golan Heights.
Smoke from artillery shelling rises above Jbatha Al-khashab.
An armed Syrian rebel wearing the jersey of FC Barcelona rests with comrades near the northern city of Aleppo on Sunday. The rebel Free Syrian Army announced the start of the battle to “liberate” Aleppo, Syria’s commercial hub and a traditional bastion of President Bashar al-Assad’s regime.
A Free Syrian Army soldier rips a portrait of President Bashar al-Assad at the Bab Al-Salam border crossing to Turkey on Sunday.
Dozens of Turkish truck drivers on Saturday, July 21, accused Free Syrian Army rebels of having burned and looted their lorries as they captured Syria’s Bab al-Hawa post, near Aleppo, from government troops.
In this photo released by the Shaam News Network, a truck burns after shelling in the Erbeen suburb of Damascus on Saturday, July 21.
Refugees fleeing the violence in Syria arrive by bus in Baghdad, Iraq, on Saturday.
Turkish soldiers stand guard at the Cilvegozu border gate in Reyhanly that connects to Syria’s Bab al-Hawa post. An estimated 120,000 people have fled Syria to Turkey, Iraq, Lebanon and Jordan.
Burned-out trucks at the Bab al-Hawa Syrian border post with Turkey on Friday, July 20. Syrian rebels seized control of the post after a fierce battle with Syrian troops, an AFP photographer at the scene reported.
Syrian soldiers celebrate in the al-Midan area in Damascus on Friday. Syrian regime forces routed rebel fighters from the Damascus neighbourhood of Midan, Syrian state television reported, saying troops had “cleaned” the district of “terrorists.”
Journalists are shown a dead body on a government tour of the al-Midan area in Damascus on Friday.
Members of Syria security forces rest in the al-Midan area in Damascus on Friday.
Syrian army soldiers hang their national flag in a partially destroyed neighborhood in the al-Midan area in Damascus.
Smoke hangs in the air in a partially destroyed neighborhood in the al-Midan area in Damascus.
Members of Syria security forces pose for photographers in the al-Midan area in Damascus after driving out the rebel fighters.
Syrian residents take goods from a truck that rebels captured at the Bab al-Hawa border crossing with Turkey on Friday.
A picture released by the official Syrian Arab News Agency on July 19 shows Syrian General Fahd al-Freij meeting with President Bashar al-Assad in Damascus after his swearing-in ceremony as defense minister.
A man holds up a picture of President Bashar al-Assad at a former police station in Atareb after clashes between Syrian soldiers and Free Syrain Army near Aleppo on Thursday, July 19. Rebels seized control of border crossings with Iraq on Thursday, dealing a new blow to al-Assad, as China and Russia dismayed the West by blocking U.N. action against his regime.
People walk along the street in Atareb amidst damage caused by clashed between Syrian soldiers and the Free Syrian Army.
A Syrian man checks the former police station of Syrian regime after a clash at Atareb on Thursday.
Smoke ascends from from alleged shelling of the Syrian village of Jebata al-Khashab as seen from the hill village of Buqaata in the Israeli-annexed Golan Heights on Thursday.
The death toll in Syria on July 12 reached 287, making it the bloodiest day in Syria since the uprising began. As it has done consistently, Syrian state television blamed “armed terrorist groups” for the killings.
A Syrian woman sits with her grandson outside a damaged building after attacks in the Syrian village of Treimsa on July 13, 2012. More than 200 people were massacred in the town, according to activists.
A Syrian demonstrator holds an opposition flag during a protest in Damascus on July 2, 2012. There have been increasing reports of violence in the Syrian capital.
Syria’s President Bashar al-Assad waves as he arrives for a speech to Syria’s parliament in Damascus on June 3, 2012. The embattled president denied that government forces were behind the “outrageous” massacre in Houla.
People gather at a mass burial on May 26, 2012 for victims reportedly killed during an artillery barrage from Syrian forces in Houla. The attack left at least 108 people dead, including nearly 50 children, according to the United Nations.
Members of the Free Syrian Army return to Qusayr on May 12, 2012 after an attack on Syrian regime forces in the village of Nizareer, near the Lebanese border in Homs.
A U.N. observer speaks with Syrian rebels and civilians in the village of Azzara on May 4, 2012, days before the country’s parlianemtary polls were held against a backdrop of unrest.
Thousands of Syrians wave their national flag and hold portraits of President Bashar al-Assad and Lebanon’s Hezbollah chief Hassan Nasrallah, right, during a rally to show support for their leader on March 29, 2012 in Damascus.
Syrian rebel fighters man a checkpoint leading into the town of Taftanaz in the rebel stronghold province of Idlib on March 20, 2012.
A Free Syrian Army rebel mounts his steed in the Al-Shatouria village near the Turkish border in northwestern Syria on March 16, 2012, a year after the uprising began. The Free Syrian Army is an armed opposition group made up largely of military defectors.
Syrian refugees walk across a field before crossing into Turkey on March 14, 2012. International mediator Kofi Annan called for an immediate halt to the killing of civilians in Syria as he arrived in Turkey for talks on the crisis.
A day after the twin suicide bombings, Syrian mourners pray over the coffins of the 44 people killed during a mass funeral in Damascus.
A Syrian man who was wounded in a suicide attack rests at a hospital in Damascus on December 23, 2011. Suicide bombers hit two security service bases in the Syrian capital, killing dozens of people.
Arab foreign ministers attend an emergency meeting at the Arab League headquarters in Cairo on October 16, 2011, to discuss the crisis in Syria.
U.S. Secretary of State Hillary Clinton speaks to the media in Washington on August 18, 2011. Clinton said U.S. sanctions on Syrian oil “strike at the heart of the Syrian regime.”
Syrian youths wave national flags while army troops drive out of Daraa on May 5, 2011. During a week-long military lockdown of the town, dozens of people were reportedly killed in what activists described as “indiscriminate” shelling on the city.
Syrians in Damascus protest in the street on March 25, 2011, after clashes with government forces in Daraa left several dead.
Supporters of Syrian President Bashar al-Assad rally on April 1 in Istanbul, Turkey, as delegates from dozens of countries gather to push for ways to end the deadly violence in Syria. The United Nations estimates more than 10,000 people have been killed since the beginning of the crisis in March 2011. The conflict is now being labeled a civil war by the International Committee of the Red Cross.
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“We have communicated in no uncertain terms with every player in the region that that’s a red line for us and that there would be enormous consequences if we start seeing movement on the chemical weapons front or the use of chemical weapons.”
Obama’s remarks appeared to ratchet up his stance on the matter. Last month, talking about Syrian forces, he told a VFW convention, “They will be held accountable by the international community and the United States should they make the tragic mistake of using those weapons.”
The Syrian regime “probably has the largest and most advanced chemical warfare program in the Arab world,” Michael Eisenstadt, director of the military and security studies program at the Washington Institute for Near East Policy, told CNN last month.
It includes “thousands of tube and rocket artillery rounds filled with mustard-type blister agents, thousands of bombs filled with the nerve agents sarin and possibly VX, and binary-type and cluster CW warheads filled with nerve agents for all its major missile systems.
“Its CW infrastructure is believed to include several production facilities and numerous storage sites, mostly dispersed throughout the western half of the country,” Eisenstadt said.
Syria is thought to have a biological warfare research and development program, but is not known to have offensive biological warfare agents, Eisenstadt said.
The nation is not a party to the Organization for the Prohibition of Chemical Weapons. That’s the body of the Chemical Weapons Convention dedicated to eliminating the weapons.
Israeli President Shimon Peres has said his country too is preparing contingency plans to attack Syria’s chemical weapons arsenal if Israel is directly threatened. In September 2007, Israeli jets bombed a building in Syria that the U.N. nuclear agency eventually concluded was “very likely a nuclear reactor.”
Obama’s warning on Monday came as Muslims in Syria celebrated the second of three days of feasting to honor the end of the holy month of Ramadan, with the holiday’s message of amity and tolerance contrasting sharply with reality.
At least 150 people were killed Monday, including two children and their mother in Daraa, the opposition Local Coordination Committees of Syria said.
A Japanese journalist was killed during a gun battle in Aleppo, the Japanese foreign ministry said Tuesday.
Mika Yamamoto, 45, worked for the independent Japan Press news agency and had been reporting on the Free Syrian Army. Her body was taken to Turkey, where officials were working to get more information, the ministry said.
Also among the dead in Syria were 10 bodies discovered splayed on the ground in the Damascus suburb of Qaboun. Video posted by activists showed at least one of the victims lying on his back, blindfolded, his arms stretched above his head. Others showed victims with bruised flesh and dark red splotches on their clothes. CNN cannot authenticate the video.
Another video, said to have been shot Sunday in the town of Talbeesa, north of Homs, showed children being pushed on swings. The swings are attached to the gun of a tank on which adults are standing, chanting, “Victory for the rebels!”
In a third video, showing the same tank, a man says to the camera, “We will enter Homs with this tank and liberate all of Syria, God willing!”
Daraa province, where the conflict began in March 2011 as peaceful anti-government demonstrations, has suffered heightened violence in recent days.
It is also the home province of Vice President Farouq al-Sharaa, who rebels say has defected from the regime.
On Sunday, the charred bodies of 20 people were discovered in the Daraa city of Hirak, and 31 other people were killed in the province, the LCC said. Government forces executed 14 people in Daraa hours after they were detained, the opposition network said.
Hirak took another beating Monday, when mortars and rockets rained down on the city, the LCC said.
Since the Syrian crisis began 17 months ago, more than 20,000 people — most of them civilians — have been killed, opposition activists say.