"This is a violation of a long-held international norm that bans the use of chemical weapons on a widespread scale," Carney told reporters. "I'm not going to lay out a legal case here because we are evaluating potential responses."
Carney spoke shortly after Secretary of State
The president shared those sentiments, Carney told reporters, although the spokesman did not specifically say whether Obama had viewed the videos posted online by antigovernment protesters.
The Syrian opposition says hundreds of people were killed in the Aug. 21 attack, which they blame on the government of President
The White House believes "there is very little doubt" that Assad is responsible for the attack, Carney said.
He said the administration would present evidence "in the coming days," but did not say whether such a presentation would be a prelude to some form of action.
The White House is considering a military response to the attack, including possible missile strikes on targets within Syria.
Asked whether Obama intended his decision to turn the tide of the 2 1/2-year-old civil war, Carney stressed that the action would be a "response" to the chemical attack and "distinct" from U.S. support for some of the rebel forces trying to oust Assad.
Neither side in Syria admits to using chemical weapons. U.N. weapons inspectors on Monday visited one of the towns that was allegedly targeted. But their mandate is limited to determining whether chemical agents were used, not apportioning responsibility.