Assad has denied using chemical weapons, calling the allegations ‘‘preposterous.’’
‘‘Allowing the use of chemical weapons on a significant scale to take place without a response would present a significant challenge to, threat to, the United States’ national security,’’ White House spokesman Jay Carney said Tuesday.
The US and its international partners were unlikely to undertake military action before Thursday. That’s when British Prime Minister David Cameron will convene an emergency meeting of Parliament, where lawmakers are expected to vote on a motion clearing the way for a British response.
The prime minister’s office said Wednesday that it will put forward a resolution to the UN Security Council condemning the Syrian government for the alleged chemical attack.
Obama and Cameron spoke Tuesday, and a Cameron spokesman said the two leaders agreed that a chemical attack had taken place, and that the Assad regime was responsible.
Also Tuesday, Vice President Joe Biden became the highest-ranking US official to publicly charge that Assad’s government fired chemical weapons last week near Damascus.
‘‘There’s no doubt who is responsible for this heinous use of chemical weapons in Syria: the Syrian regime,’’ Biden said.
Ahead of any strike, the US also planned to release additional intelligence it said would directly link Assad to the attack in the Damascus suburbs. Syrian activists said hundreds of people were killed in the attack. A US official said the intelligence report was expected to include ‘‘signals intelligence’’ — information gathered from intercepted communications.
Even before releasing that information, US officials said Assad was culpable in the attack, based on witness reports, information on the number of victims and the symptoms of those killed or injured, and intelligence showing the Syrian government has not lost control of its chemical weapons stockpiles.
AP National Security Writer Robert Burns reported from Bander Seri Begawan, Brunei. Lolita C. Baldor in Washington contributed to this report.