Syria is believed to have around 1,000 metric tonnes of chemical toxins and has agreed to destroy them under a joint Russian-US proposal.
The Organisation for the Prohibition of Chemical Weapons (OPCW) said the letter was being assessed against its requirements. It also said it was indefinitely postponed a Sunday meeting to discuss a Russia-US plan to destroy Syria's arsenal.
"The meeting of the Executive Council of the OPCW in regard to Syria, scheduled for Sunday has been postponed," the Hague-based Organisation for the Prohibition of Chemical Weapons said. "We will announce the new date and time in this space as soon as possible," The Hague-based organisation added.
Diplomatic sources said that a draft text to be discussed at the meeting had not yet been agreed upon by the United States and Russia.
After action by the 41-member executive council of the OPCW, a Security Council resolution will be needed to override some provisions of the international Chemical Weapons Convention to allow an effort to find, transport and dismantle chemical arms in the middle of a civil war.
The chemical arms agency's decision must be approved by a simple majority of council members, though agreement is almost always reached through a consensus, which is expected in Syria's case. The council meets behind closed doors, but may be open to observer countries that are not yet members. Syria is not yet a full member.
As soon as the OPCW decision is made, the full UN Security Council will begin negotiations on a resolution intended to support the OPCW Executive Council's decision. The five permanent UN Security Council members have been negotiating for several days on a draft resolution.