WASHINGTON: President Barack Obama dramatically told Syria's President Bashar al-Assad Monday not to turn chemical weapons on his own people, following US warnings his forces were mixing deadly sarin gas.
Obama publicly told the increasingly beleaguered Assad not to unleash the "worst weapons of the 20th Century" in the 21st, capping a day of alarming American warnings on the Syrian regime's intentions.
"Today, I want to make it absolutely clear to Assad and those under his command, the world is watching, the use of chemical weapons is and would be totally unacceptable," Obama said.
"If you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable."
The Damascus government, hitting back at increasingly explicit US rhetoric, had earlier pledged never to take such a step, which the Obama administration warns would cross a "red line" and result in US action.
Adding to the impression of a quickening endgame in Syria, Arab League chief Nabil al-Arabi exclusively told AFP that Assad's regime was in danger of collapse "anytime" as the opposition makes sweeping gains.
And prompted by deteriorating security, the United Nations suspended operations in Syria and said it would pull out non-essential staff, while the European Union reduced its activities in Damascus to a minimum.
A US official told AFP earlier that Syria had begun mixing chemicals that could be used to make sarin, a deadly nerve agent, while CNN reported Damascus may mull the use of the gas in a limited artillery attack on advancing rebels.
The intelligence appeared to explain a series of fresh warnings issued by Washington that the use of chemical weapons by the Assad government would invite unspecified US action.
The White House has been loath to make a direct intervention in Syria but indicated Monday that the use of chemical weapons could change the equation.
"We are concerned that an increasingly beleaguered regime, having found its escalation of violence through conventional means inadequate, might be considering the use of chemical weapons against the Syrian people," White House spokesman Jay Carney said.
Washington worries that battlefield advances by rebels could prompt Assad to use chemical arms, or that such stocks could become insecure or find their way into the hands of groups hostile to the United States and allies.
In televised remarks, an unnamed Syrian foreign ministry official said Syria would "never, under any circumstances, use chemical weapons against its own people, if such weapons exist."
The New York Times reported that as well as public warnings to Assad, US and European officials had sent private warnings to Damascus through Russia.
Secretary of State Hillary Clinton, during a trip to Prague, declined to "telegraph" what Washington would do if Syria crossed its "red line" and used chemical weapons.
But she said: "Suffice it to say that we're certainly planning to take action if that eventuality were to occur."
A 150-strong US task force, including special forces soldiers, has been stationed in Jordan for several months, and could be called into action if Syria loses control of its chemical weapons amid battlefield chaos.
In Syria itself, there were new developments in a vicious conflict that has taken an estimated 41,000 lives since erupting in March 2011.
In an exclusive interview with AFP, Arabi said Assad's regime was in danger of collapse "anytime" as the opposition made political and military headway.
"Facts on the ground indicate very clearly now that the Syrian opposition is gaining, politically and militarily. Every day they are gaining something," Arabi said.
In another blow to the Assad regime, foreign ministry spokesman Jihad Makdisi, a prominent advocate of the president, was reported to have quit and headed for London from Beirut.
UN spokesman Martin Nesirky said the world body would pull non-essential international staff from Syria with "immediate effect."
The EU said it was also reducing activities in Damascus to a minimum.
An air strike Monday killed at least 12 people -- eight rebels and four civilians -- and wounded more than 30 in the rebel-held town of Ras al-Ain on the border with Turkey, the Syrian Observatory for Human Rights said.
The monitoring group, which relies on a network of activists and medics in civilian and military hospitals, said 86 people -- including 32 civilians, 32 rebels and 22 troops -- were killed Monday as Syrian troops battered rebel positions in and around Damascus.
On the diplomatic front, Russian President Vladimir Putin warned Turkey that the NATO deployment of Patriot missiles along its border with Syria could exacerbate tensions after meeting Turkish Prime Minister Recep Tayyip Erdogan.
Russia objects to Turkey's NATO request for the deployment of Patriot missiles as Assad's regime clings to power and suppresses a rebellion.
Moscow has warned that such a deployment could spark a broader conflict, pulling in the Western military alliance.
"As they say, if a gun is hung on the wall at the start of a play, then at the end of the play it will definitely fire," Putin said.