REUTERS/Andrew Winning
U.S. President Barack Obama walks with
The abrupt halt in British momentum towards military action left the diplomatic choreography in chaos and US officials "livid" with the British, according to Western diplomatic sources at the United Nations in New York.
However US officials said on Thursday Mr Obama would not be constrained by waiting for a British parliamentary vote or by trying to forge a consensus at the United Nations where an "intransigent" Russia has made clear it would veto any resolution to use force.
Asked whether the US would "go it alone" without Britain, a White House spokesman quoted William Hague saying that the US was "able to make their own decisions", adding that the administration appreciated UK support for a strong response to the chemical weapons attacks.
"We've also seen an acknowledgement from the Foreign Secretary about the United States' right and ability to make our own foreign policy decisions that are in our national security interest," said Josh Earnest, the White House deputy press secretary.
Mr Obama, who spoke with some senior members of the US congress on the Syria debate, is due to leave for Sweden next Tuesday, followed by the G20 summit in Russia on Thursday and Friday, potentially narrowing the timetable for action.
Analysts said the Mr Obama was highly unlikely to unleash the targeted missile strikes while alongside the Russian President Vladimir Putin, forcing a choice of acting either before next Tuesday or after the G20 summit closes next weekend.
"Why would you launch when Putin is sitting there? You either go before the trip to Russia or after and my guess is before," said Barry Pavel, a former White House defence official, adding the US could launch attacks over the weekend once UN inspectors have left Damascus.
"Britain is important diplomatically, but not required, and not required militarily. The White House could move ahead without the British," Mr Pavel added.
Ban Ki-Moon, the UN Secretary-General, said on Thursday the UN inspection team in Syria would finish its work on Friday and meet him in New York on Saturday to discuss their findings.
Mr Ban confirmed their timetable after speaking on the telephone to Mr Obama when he urged the US president to allow the inspectors to finish their work and report back. "I told him [Mr Obama] that we will surely share our information and our analysis," he said.
The White House, however, said that the UN inspectors' mandate was not to allocate blame but only to establish whether chemical weapons had been used – a fact that had been agreed to by all sides.
Mr Obama's dilemma over whether to act without direct British support follows Mr Cameron's embarrassing climb-down on Wednesday over whether a Commons vote would be required to sanction UK military involvement.
"The Americans are livid with us," said one Western diplomat, who added British officials were astonished that the Prime Minister could have made such an "enormous miscalculation" amid such high stakes.
A furious-looking Samantha Power, the US ambassador to the UN, refused to answer questions on Thursday as she left a meeting of the Security Council permanent members, but later said on Twitter that the Syrian regime "must be held accountable, which the Security Council has refused to do for two years", adding "The US is considering an appropriate response."
Mr Obama said on Wednesday there was "no doubt" the Assad regime was behind the chemical weapons attacks that killed at least 350 people, arguing that a "limited" strike would send a clear message to Assad to "stop doing this" and be beneficial to long-term US national security interests.
The administration said it was preparing to publish a declassified intelligence dossier last night. Officials told the Associated Press that the assessment was not a "slam dunk", however Mr Earnest said that both Democrat and Republican senators briefed on the classified intelligence had accepted that Assad was responsible for the attacks.
"I have no interest in any open-ended conflict in Syria, but we do have to make sure that when countries break international norms on weapons like chemical weapons that could threaten us, that they are held accountable," Mr Obama told the US Public Broadcasting Service (PBS).
However high profile voices, including the Republican speaker of the House John Boehner and Donald Rumsfeld, the former Defense Secretary who was the architect of intervention in Iraq, said the administration not yet properly justified an attack on Syria.
"There really hasn't been any indication from the administration as to what our national interest is with respect to this particular situation," Mr Rumsfeld told Fox News, adding that Mr Obama's indecision over Syria over the last two years had left a "vacuum" in the Middle East.
Seeking to justify the national security interest, Mr Obama also said that the US could be at direct risk of proliferation of Syrian chemical weapons, a contention that was challenged by those opposing military action.
Although facing calls from some members of Congress for a British-style debate on whether to take military action, Mr Obama is not constrained in the same way as a British prime minister.
Senate aides told The Daily Telegraph that Congress was split three ways on Syria, between anti-war Democrats and isolationist conservatives against action, hawkish neo-conservatives who want to see Assad forcibly removed and an emerging middle ground.
"This emerging third group supports a limited strike targeting the unit or brigade responsible for the chemical weapons strike," the aide said, "and as with all things, the middle ground is usually where the American people are."