The Obama administration is gearing up for the biggest foreign policy vote in Congress since the Iraq war by arguing that new physical evidence shows the Syrian government used sarin gas in a deadly August attack.
In a series of TV news interviews Sunday, Secretary of State John Kerry presented President Barack Obama's case for military action.
He outlined the latest information the administration has received about the Aug. 21 attack in the Damascus suburbs that the U.S. says killed 1,429 civilians, including more than 400 children.
He said hair and blood samples collected by first responders have added to the growing body of proof that Syria's government launched a chemical weapons attack.
Also on Sunday, senior U.S. officials laid out their case to lawmakers in a classified briefing.
Congress is set to take up the Syrian issue when it returns from a summer break on Sept. 9.
Kerry said he's confident Congress will give the president its backing for a military strike. But he also said the president has authority to act on his own if Congress doesn't give its approval.