An elite Syrian unit that runs the government's chemical arms program has been scattering the weapons to dozens of sites across the country, potentially complicating U.S. plans for air strikes, the Wall Street Journal reported.
The newspaper, citing unnamed U.S. officials and lawmakers briefed on the intelligence, said on its website on Thursday that a secretive military group known as Unit 450 had been moving the stocks around for months to help avoid detection of the weapons.
U.S. and Israeli intelligence agencies and Middle Eastern officials still believe they know the location of most of the government's chemical weapons supply, the Journal said.
But "we know a lot less than we did six months ago about where the chemical weapons are," one official was quoted as saying.
The United States and its allies say Syrian President Bashar al-Assad's forces carried out a chemical weapons attack in a Damascus neighborhood on Aug. 21 that U.S. officials say killed about 1,400 people, including 400 children. Assad and Syrian ally Russia blame rebel forces.
The United States and Russia began high-stakes talks on Thursday on Moscow's plan for Syria to surrender its chemical weapons as Damascus formally applied to join a global poison gas ban.
The talks were part of a diplomatic push that prompted President Barack Obama to put on hold plans for U.S. air strikes in response to the suspected attack.
The United Nations said it received a document from Syria on joining the global anti-chemical weapons treaty, a move Assad promised as part of a deal to avoid U.S. air strikes.
Syria's civil war has killed more than 100,000 people since 2011.
The Journal quoted a senior U.S. official as saying that Washington estimated that Damascus had 1,000 tonnes of chemical and biological agents, "although there might be more."
After traditionally storing most of its chemical and biological weapons at a few sites in western Syria, the government started dispersing the weapons about a year ago, officials said.
They added that the United States now believed the arsenal had been moved to up to 50 sites in the west, north, south and east of the country.
No decision had been made whether to target commanders of the small unit, made up of officers from Assad's Alawite sect, the paper said, quoting a senior U.S. official.
There were also no plans to bomb chemical weapons sites directly because of the potential risk that poisons could be dispersed to civilian areas, officials told the paper.