France on Tuesday joined the United States and NATO in delivering a blunt warning to Damascus not to use chemical weapons on rebels, warning that the international community would react if it did.
"Any use of these chemical weapons by (Syrian President Bashar) al-Assad would be unacceptable," foreign ministry spokesperson Vincent Floreani told reporters.
"The leaders in Damascus must know the international community is watching them and will react" if they are used, he said, adding that France was in contact with its partners to "prevent any use of these arms should the regime or anyone else be tempted".
US President Barack Obama on Monday told Assad not to use chemical weapons against his own people, in a new warning as the conflict approaches the 21-month mark with more than 41 000 people killed.
The Syrian government, fighting to prevent the capital Damascus from falling to rebel forces, reiterated on Monday that it would never resort to chemical weapons.
But a US official told AFP that Syria had begun mixing chemicals that could be used to make sarin, a deadly nerve agent, while CNN reported Damascus could use the gas in a limited artillery attack on advancing rebels.
Washington fears that battlefield advances by rebels could prompt Assad to use chemical arms, or that such stocks could become insecure or find their way into the hands of groups hostile to the United States and its allies.
NATO on Tuesday joined Washington in delivering a blunt warning to Damascus against the use of chemical weapons, as the alliance readied to approve a Turkish request for missiles to protect its border with Syria.