US warns Syria against using chemical weapons

US President Barack Obama has warned Syria's President Bashar al-Assad it would be a "tragic mistake" to unleash chemical weapons, after Damascus threatened to use them if attacked.

At a Damascus news conference Monday, foreign ministry spokesman Jihad Makdissi said Syria has chemical weapons and will use them if attacked by outsiders, though not against its own civilians.

Makdissi's remarks came amid growing international concern that Damascus is preparing to deploy its chemical arsenal in the repression of a 16-month uprising against the Assad regime.

"Syria will not use any chemical or other unconventional weapons against its civilians, and will only use them in case of external aggression," Makdissi told reporters.

"Any stocks of chemical weapons that may exist, will never, ever be used against the Syrian people," he said, adding that in the event of foreign attack, "the generals will be deciding when and how we use them."

But President Obama immediately intervened, warning Assad not to make the "tragic mistake".

"Given the regime's stockpile of chemical weapons, we will continue to make it clear to Assad and those around him that the world is watching," Obama said.

"They will be held accountable by the international community and the United States should they make the tragic mistake of using those weapons," he added.

Israel has also warned it could take military action if any of its advanced weapons end up in the hands of Hezbollah.