US unable to determine Syria chemical weapons use: official

The United States said today it has yet to "conclusively determine" that chemical weapons were used in an attack in Syria that allegedly killed hundreds of people.

State Department spokeswoman Jen Psaki said President Barack Obama had directed US intelligence to gather information about the reported attack near Damascus.

"At this time right now, we are unable to conclusively determine CW use, but we are focused every minute of every day since these events happened yesterday on doing everything possible within our power to nail down the facts," Psaki said.

The main Syrian opposition group has charged that as many as 1,300 people were killed in a chemical weapons attack yesterday near Damascus.

Obama has said that chemical weapons use by the Syrian regime would cross a US "red line," but Washington so far has not acted on earlier reports of chemical weapons attacks.

"If these reports are true, it would be an outrageous and flagrant escalation of use of chemical weapons by the regime," Psaki said.

"The president of course has a range of options that we've talked about before that he can certainly consider and of course discuss with his national security team," she said.