The United States is increasingly focused on how to secure Syria’s chemical weapons if President Bashar al-Assad falls from power, Defense Secretary Leon Panetta said Thursday, AFP reports.

Panetta said he would not consider sending ground troops into the war-torn country, even to secure chemical sites, but he left the door open to some U.S. military presence if Assad’s downfall is followed by a peaceful transition.

While the U.S. government has issued stern warnings to Damascus against resorting to chemical weaponry in its war with rebel forces, Panetta said the greater risk might be a chaotic vacuum if Assad is toppled.

“I think the greater concern right now is what steps does the international community take to make sure that when Assad comes down, that there is a process and procedure to make sure we get our hands on securing those sites,” he said, according to AFP.

“That, I think, is the greater challenge right now.”

The U.S. government was discussing the issue with Israel and other countries in the region, he said, but ruled out deploying American ground forces in any “hostile” setting.

“We’re not talking about ground troops,” Panetta insisted, adding that any future U.S. military role in Syria would only come about if a new government asked for assistance.

“You always have to keep the possibility that, if there is a peaceful transition and international organizations get involved, that they might ask for assistance in that situation,” he said.

“But in a hostile situation, we’re not planning for that.”

The U.S. military’s top officer, General Martin Dempsey, told the same news conference that if Assad chose to use his chemical stockpiles against opposition forces, it would be virtually impossible to stop him.

He said preventing the use of chemical arms “would be almost unachievable… because you would have to have such clarity of intelligence, you know, persistent surveillance, you would have to actually see it before it happened.”

“And that’s unlikely, to be sure.”

Dempsey said that clearly worded warnings to Assad from President Barack Obama have served as a deterrent.

Syria’s chemical weapons stockpile, which dates back to the 1970s, is the biggest in the Middle East, but its precise scope remains unclear, according to analysts.

The country has hundreds of tons of various chemical agents, including sarin and VX nerve agents, as well as older blistering agents such as mustard gas, dispersed in dozens of manufacturing and storage sites, experts say.

U.S. officials recently said there was evidence that Syrian President Bashar Al-Assad’s troops had not only moved deadly sarin gas that might be used against rebels, but also that its binary components, usually stored separately, had been combined and placed into bombs for use.

Doctors have said that Assad’s forces are probably also using “Agent 15,” which causes paralysis.

The United States and its allies, including Israel, have repeatedly expressed concern that Syria’s stockpile, believed to be one of the biggest in the world, could be stolen and fall into extremist hands or be transferred to the Hizbullah terror group by a crumbling Syrian regime.