"Legally speaking Syria has become, starting today [Thursday], a full member of the (chemical weapons) convention," Syrian UN Ambassador Bashar al-Ja'afari told reporters in New York after submitting relevant documents to the United Nations on Thursday.
Syria agreed to the plan after the United States threatened military strike on the pretext of an alleged August 21 gas attack that killed hundreds of people.
The Syrian government blames the rebels for that attack. Washington claims the Syrian army used the sarin gas in the attack.
UN Secretary-General Ban Ki-moon's press office confirmed receipt of a letter from Syria that said Damascus would immediately begin complying with the terms of the treaty.
Meanwhile, Erin Pelton, spokeswoman for the US mission to the United Nations, tried to downplay the positive move by the Syrian government, saying that Syria's declared intention to join the Chemical Weapons Convention was just a first step.
"This long overdue step does not address the pressing and immediate need for a mechanism to identify, verify, secure and ultimately destroy Syria's chemical weapons stockpile so they can never again be used," Pelton claimed. "It also does not include immediate consequences for non-compliance."
"I think there are a few more steps they have to take (before Syria is a signatory) but that's why we're studying the document," a UN official said on condition of anonymity.
US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov met in Geneva to try to hammer out the details of a Russian plan for Syria to place its chemical arsenal under international control.
According to the Chemical Weapons Convention, a country does not become a full member of the treaty until 30 days after its accession or ratification documents are deposited with the United Nations.