The U.S. has strong indications that chemical weapons were not used in the attack in Syria's Aleppo province on Tuesday, a U.S. administration official said Thursday.
While officials won't entirely rule out the possibility, the official said that additional intelligence-gathering in recent days has led the U.S. to believe more strongly that it was not a weaponized chemical attack. The official wasn't authorized to speak publicly about the matter because it involved intelligence gathering and spoke on condition of anonymity.
The U.S. and allies have been looking into allegations by the Syrian regime that rebels carried out a chemical weapons attack on Khan al-Assal village in northern Aleppo province. The rebels have blamed regime forces.
U.S. officials said they were able to determine that an attack did take place in that area. Officials, however, did not rule out the possibility that some type of nonlethal chemical — which could include riot control or tear gas-type materials — might have been used.
Syria is widely believed to have a large stockpile of chemical weapons. And, there are fears President Bashar Assad would use those weapons against his people in the ongoing civil war and also concerns that al-Qaida-linked rebels might obtain and use them.
The United Nations announced Thursday that it would investigate the possible use of chemical weapons in Syria, which would amount to a crime against humanity. The probe could also help determine the security of the weapons stockpile.
Intelligence reports late last year showed the Syrian regime may be readying its chemical weapons and could be desperate enough to use them. Those reports prompted a sharp warning from President Barack Obama, who said that Syria's use or movement of its chemical weapons stockpile would change his "calculus" about whether the U.S. might intervene militarily in the conflict.
Although officials won't detail the latest intelligence that was gathered, the U.S. and its allies are generally able to use information from surveillance, intercepted communications, people at the scene, medical and autopsy reports, and soil samples, if available.
Syria is believed to have hundreds, if not thousands, of tons of chemical agents, including mustard gas, a blistering agent, and the more lethal nerve agents sarin and VX.