The U.S. government says it now has conclusive evidence that Syrian troops have used chemical weapons against rebels -- a move President Barack Obama has said would cross a "red line."
Deputy National Security Adviser Ben Rhodes told reporters Thursday that according to intelligence, as many as 150 people have died from multiple small-scale chemical weapons attacks over the past year. He said those numbers are likely not complete.
Rhodes said sarin gas is among the chemicals used by the Syrian army. And he said there is no reliable corroborated reports that the rebels also have acquired or have used chemical weapons.
U.S. intelligence officials have been saying for months they were confident that chemical weapons had been used by the Syrian government . But Mr. Obama had said he needed to see firm evidence before deciding his next move.
The White House says Mr. Obama is considering both political and military options, but it is not yet clear how quickly new actions will be taken or what they will involve.
The president is coming under increasing pressure from some in Congress and other prominent voices, including former President Bill Clinton, to take more forceful action in Syria -- including arming the rebels.
The United Nations says nearly 93,000 people have been been killed in syria over the last two years. The majority have been civilians.