Syria on Monday "categorically" denied using chemical weapons including chlorine gas in its four-year civil war, telling a global watchdog it is cooperating fully with efforts to destroy its stockpile.

"We wish here to state categorically that we have never used chlorine or any other toxic chemicals during any incidents or any other operations in the Syrian Arab Republic since the beginning of the crisis and up to this very day," Deputy Foreign Minister Fayssal Mekdad told the annual meeting of the Organisation for the Prohibition of Chemical Weapons.