Secretary of State John Kerry says that tests have shown evidence of Syria's use of the chemical agent sarin in an attack on the opposition last month that the White House has blamed on the regime of President Bashar al-Assad.
"I can share with you today that blood and hair samples that have come to us through an appropriate chain of custody from east Damascus, from first responders, it has tested positive for signatures of sarin," Kerry told CNN on Sunday.
"Each day that goes by, this case is even stronger," he said on the cable network's State of the Union program.
Kerry said the U.S. obtained the samples "independently," giving no indication the results came from the United Nations chemical weapons inspectors, who left Syria with samples on Saturday.
The U.N. has not said how long it would take to test its samples, but speaking on Saturday, a spokesman for Secretary-General Ban Ki-moon suggested it might days or a week.
