US President Barack Obama said on Monday that Syrian President Bashar Assad would be held accountable if he made the "tragic mistake" of using his stockpile of chemical weapons.
"Today we're also working so that the Syrian people can have a better future, free of the Assad regime," Obama said in a speech on his foreign policy to veterans in Reno, Nevada.
"Given the regime's stockpiles of chemical weapons, we will continue to make it clear to Assad and those around him that the world is watching and that they will be held accountable by the international community and the United States should they make the tragic mistake of using those weapons," he said.
Syria said on Monday it could use chemical weapons in response to any "external aggression" but they would not be used in Syrian President Bashar Assad's campaign to crush a 16-month-old uprising against his rule.
Obama's comments echoed a similar statement made Monday by British Foreign Secretary William Hague, who called Syria's threat to use chemical weapons against foreign intervention "unacceptable."
"This is typical of the complete illusion of this regime, that they are the victims of external aggression," Hague told reporters at a European Union foreign ministers' meeting in Brussels. "What is actually happening is their own people are rising up against a brutal police state ... and in any case it is unacceptable to say that they would use chemical weapons under any circumstances."
Foreign Ministry spokesman Jihad Makdissi said any chemical or bacterial weapons were securely stored by the armed forces.
"The ministry wants to re-affirm the stance of the Syrian Arab Republic that any chemical or bacterial weapon will never be used - and I repeat will never be used - during the crisis in Syria regardless of the developments," Makdissi said.
"These weapons are stored and secured by Syrian military forces and under its direct supervision and will never be used unless Syria faces external aggression."
It appeared to be the first time that Syria acknowledged it might possess non-conventional weapons. Damascus is not a signatory to the 1992 Chemical Weapons Convention that bans their use, production or stockpiling.
Makdissi raised the possibility that "terrorists groups" might be supplied with biological weapons by outside powers which "could be used in one of the villages - God forbid - and then they would accuse the Syrian forces."
He also said the security situation in Damascus, where Assad's forces have been battling rebels for more than a week, was improving and would return to normal within days.
He condemned calls for Assad to step down at a meeting of Arab foreign ministers in Qatar over the weekend, calling it a "flagrant intervention" in Syria's internal affairs.