Syria is seeking membership of the global convention banning chemical weapons, in a move that could help head off a western military strike.
Damascus says it now considers itself a full member of the convention. While UN leader Ban Ki-moon has welcomed the application, the United Nations did not immediately confirm it had been accepted.
Diplomats, speaking on condition of anonymity, said it was possible there were missing elements and the application could be sent back to President Bashar al-Assad.
"The Syrian letter is currently being studied and until that is completed we don't have anything to say about its status as an instrument of accession," UN spokesman Farhan Haq told AFP.
The United States, which is in talks with Russia on a plan to put Syria's chemical weapons under international control, also demanded "immediate actions" by Syria to surrender its stockpile.
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Syria had been one of seven UN members that have refused to join the 1993 convention banning the production and stockpiling of chemical arms.
Assad's government announced it will sign up as it faces a growing threat of a US military strike and Russia proposed a plan to put his country's chemical arsenal under international control.
The United States and other western nations accuse Assad forces of launching a sarin gas attack on August 21 near Damascus in which hundreds died. Washington has threatened a punitive military strike. The government blamed opposition rebels for the attack.
UN spokesman Haq said it could take a few days to complete the accession process.
But Syria's UN ambassador Bashar Jaafari says his government now considers itself a full "legal" member of the convention.
"With this, the chapter of the so-called chemical weapons should be ended," Jaafari told reporters.
"The chemical weapons in Syria are a mere deterrence against the Israeli nuclear arsenal," he added.
Under the convention, Syria has 30 days after becoming a member to declare all of its chemical weapons.

