The White House is warning the Syrian government about using chemical weapons against its their own people, saying such a move would "cross a red line."
Recent signs of increased activity at some of Syria's chemical weapons sites indicate the government may be moving some of its nonconventional weapons.
Syrian Foreign Minister Walid Muallem insisted the government would not use such weapons against its own people under any circumstances.
Secretary of State Hillary Clinton said the U.S. would "take action" should that occur.
"I'm not going to telegraph in any specifics what we would do in the event of credible evidence that the Assad regime has resorted to using chemical weapons against their own people," Clinton said, on the sidelines of meetings with Czech officials in Prague.
"But suffice it to say, we are certainly planning to take action if that eventuality were to occur," she said.
White House spokesman Jay Carney warned Syrian President Bashar Assad "the world is watching" and he will be held accountable for his actions.
"As the opposition makes strategic advances and grows in strength, the Assad regime has been unable to halt the opposition's progress through conventional means," Carney told reporters Monday. "And 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."
"They will be held accountable by the United States and the international community if they use chemical weapons or fail to meet their obligation to secure them," Carney said.
Meanwhile, the United Nations is evacuating most of its international staff from Syria.
"The security situation has become extremely difficult, including Damascus," UN regional humanitarian coordinator for Syria Radhouane Nouicer said.
Up to a quarter of the 100 international staff workers would leave Syria by the end of the week he said.