Syria's stockpile of chemical agents is largely "unweaponized" and could be eradicated more quickly than initially thought, the Washington Post reported Thursday citing a confidential US and Russian assessment.

The report said American and Russian officials now believe Syria's entire arsenal could be dismantled within a nine-month timeframe, and that the unweaponized state of the chemicals made it less likely they could be hidden or seized by terrorist organizations.

The Post cited two unnamed people who had been briefed on the analysis. The report came as the United States and Russia agreed a landmark draft UN Security Council resolution on destroying Syria's chemical weapons.

The resolution would be the first passed by the 15-member council since the start of the Syrian conflict in March 2011.

Diplomats said the resolution allows for the council to decide on sanctions against Syria's President Bashar al-Assad at a later date if a breach of a Russia-US disarmament plan is reported.

The Post reported that in private briefings to weapons experts, analysts had estimated Syria possesses more than 1,000 metric tons of chemical weapons, including 300 metric tons of sulfur mustard.

However, the remainder of the stockpile was made up of chemical precursors to nerve agents that were "unweaponized" and in "liquid bulk" form and therefore easier to destroy.

The report said two chemical precursors for sarin nerve gas needed to be blended using special equipment before being loaded into rockets or artillery shells.