U.S. State Department spokeswoman Jen Psaki said during a Thursday news briefing Washington was trying to get to "the bottom of the facts" about the alleged use of chemical weapons in Syria.
Syrian opposition groups said hundreds of people were killed in an alleged chemical weapons attack by government forces in the outskirts of Damascus. Syrian allies said the allegations were an effort by the opposition to turn international public opinion in its favor.
Psaki said the focus in Washington was to "urgently gather additional information" about the alleged attack. U.S. President Barack Obama -- who has said the use of chemical weapons in Syria would be a "red line" prompting a stern reaction -- told CNN in an interview Friday his administration is still evaluating the matter, but "what we've seen indicates that this is clearly a big event of grave concern."
"We have to think through strategically what's going to be in our long-term national interests," he said.
Catherine Ashton -- EU foreign affairs and security policy representative -- said Friday she was in support of an impartial investigation into the attack.
A U.N. team is in Syria investigating previous claims of the use of sarin nerve gas in the conflict.
"The international community must now urgently show a united face and ensure that a credible and thorough investigation can be carried out," Ashton said in a statement.
British Foreign Secretary William Hague struck a similar tone, saying it wasn't something "a humane or civilized world can ignore."
U.N. Secretary-General Ban Ki-moon in July said at least 100,000 people have died as a result of war in Syria.
"We must now put an end to the spiral of violence, terrorism and to the ever growing flow of refugees," Ashton said. "The international community must now act with a sense of urgency and responsibility."
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