U.S. and Russian officials now believe that the vast majority of Syria’s nerve agent stockpile consists of “unweaponized” liquid precursors that could be neutralized relatively quickly, lowering the risk that the toxins could be hidden away by the regime or stolen by terrorists.

A confidential assessment by the two governments also concludes that Syria’s entire arsenal could be destroyed in about nine months, assuming that Syrian officials honor promises to surrender control of its chemical assets to international inspectors, according to two people briefed on the analysis.

The assessment, thought to be the most authoritative to date, reflects the consensus view of Russian and U.S. analysts who compared their governments’ intelligence on Syria during meetings in Geneva this month. The Obama administration has since briefed independent experts on the key findings.

The insights into Syria’s arsenal have been bolstered further by the Damascus government’s own accounting, which lists the types of chemical agents and delivery systems it possesses and was presented Saturday to the Organization for the Prohibition of Chemical Weapons in The Hague. U.S. officials have reviewed the Syrian inventory, which has not been publicly released, and “found it quite good,” a senior State Department official told reporters.

In military weapons programs, two chemical precursors for sarin are blended using special equipment as the toxins are loaded into rockets, bombs or artillery shells.

The White House declined to comment on the assessments, which have been kept under wraps amid intense negotiations at the United Nations on a plan for dismantling Syria’s chemical stockpile. The five permanent members of the U.N. Security Council agreed Thursday on a resolution that requires Syria to surrender its chemical weapons.

Russia has long been a close ally and arms supplier to Syria and maintains strong ties to its military and intelligence services.

In private briefings with weapons experts, White House officials said analysts had concluded that Syria possesses more than 1,000 metric tons of chemical weapons, of which about 300 metric tons are sulfur mustard, the blister agent used in World War I. Nearly all of the remainder consists of chemical precursors of the nerve agent sarin, described as being “unweaponized” and in “liquid bulk” form, according to two people who attended White House briefings.

Weapons experts not privy to the briefings described the findings as encouraging. Several noted that it is far easier to destroy precursor chemicals than battlefield-ready liquid sarin or warheads already loaded with the toxin.

“If the vast majority of it consists of precursors in bulk form, that is very good news,” said Michael Kuhlman, chief scientist in the national security division at Battelle, a company that has supervised the destruction of much of the United States’ Cold War-era chemical stockpile. “The destruction processes for those chemicals are well in hand.”