U.S. intelligence has uncovered activities possibly related to the preparation of chemical weapons at more than one location in Syria, CNN reported on Tuesday.
An anonymous U.S. official said the Syrian military could be "cooking up recipes" for chemical arms at a "small" quantity of manufacturing sites. Other unidentified officials earlier this week told news organizations that Syrian engineers were combining the precursor agents for sarin nerve agent.
The Defense Department estimates there are more than 50 sites with roles in the Bashar Assad regime's substantive chemical weapons program, including depots, research facilities and manufacturing plants. There appears to be operations at some of the sites though there are no signs that chemical warfare materials have been removed from the facilities, multiple high-ranking U.S. armed forces sources said.
Officials declined to specify what sort of work has been detected; they said there were no indications that a Syrian chemical attack was looming.
Fighting has ramped up around Damascus in recent days, placing further pressure on the embattled regime.
"Our concerns are that an increasingly desperate Assad regime might turn to chemical weapons, or might lose control of them to one of the many groups that are now operating within Syria," Reuters quoted U.S. Secretary of State Hillary Clinton as saying on Wednesday.
"We have sent an unmistakable message that this would cross a red line and those responsible would be held to account," according to Clinton, who on Tuesday joined other NATO foreign ministers in approving deployment of Patriot air-defense batteries along Turkey's border with Syria.
Any attempt to take control of Syria's chemical stockpile would be fraught with danger for the U.S. ground troops that might have to be deployed and the risk that some chemical warfare materials would not be secured, Agence France-Presse reported..
"It's difficult to come up with a viable scenario where you do this without putting troops on the ground," Jane's Information Group analyst David Hartwell said in an interview. "If your aim is to secure chemical weapons, you can't do that from the air."
A bombing raid on chemical agent plants and weapon warehouses could lead to the unintended release of toxic materials into the environment -- putting residents in the area at risk -- and might not even result in the the total destruction of the targeted substances, Washington Institute for Near East Policy issue expert Michael Eisenstadt wrote in an analysis.
A more likely option would involve the deployment of elite units of British, French and U.S. troops to provide advice to friendly regional armed forces on how to carry out a ground assault of Assad's chemical sites. "The U.S. provides advice, the logistics, and the backup whereas the boots on the ground would be provided from somewhere else," according to Hartwell.
It has been estimated that it would require as many as 75,000 soldiers to secure Syria's chemical arms complex.
Some 150 U.S. military personnel are already in Jordan to advise the military there on how to prepare for a chemical weapons emergency, including a potential incursion against Syrian installations.
U.N. Secretary General Ban Ki-moon on Wednesday pressed Damascus to refrain from mounting chemical attacks, the Associated Press reported.
"I again urge in the strongest possible terms that they must not consider using this kind of deadly weapons of mass destruction, the U.N. chief told AP. "I have warned that if in any case this should be used, there will be huge consequences."
Israeli Prime Minister Benjamin Netanyahu on Tuesday said "we are closely following developments in Syria related to its chemical weapons stockpiles," AFP reported.
Meanwhile, the U.S. Senate on Tuesday overwhelmingly approved an amendment to the fiscal 2013 National Defense Authorization Act that would require the Defense Department to report to relevant congressional committees on the possibilities for a military intervention in Syria aimed at weakening the government's ability to use air attacks to assault opposition forces, Foreign Policy reported. The report is due within three months after the law's entry into force.