The British Prime Minister, David Cameron, has lost a vital parliamentary vote endorsing military action against Syria.
I hoped we would carry the argument but we understand there is a deep well of suspicion about involvement in the Middle East
In an unexpected development, Cameron and his coalition government failed to pass a motion that would have authorised military action against Syria in principle by 285 to 272 votes.
Thursday evening's vote was non-binding, but in practice the rejection of military strikes means Cameron's hands are tied.
The British Defence Secretary, Philip Hammond, said that Britain would not take part in any military action.
"I hoped we would carry the argument but we understand there is a deep well of suspicion about involvement in the Middle East," Hammond told a UK news channel.
The United States, a key ally, would be disappointed that Britain "will not be involved," he added, but said: "I don't expect that the lack of British participation will stop any action."
It was a stunning defeat for a government which had seemed days away from joining the US in possible attacks to punish President Bashar al-Assad's regime over an alleged chemical weapons attack.
Despite the outcome of the vote, the US said it would "continue to consult" with London, "one of our closest allies and friends".
"President Obama's decision-making will be guided by what is in the best interests of the United States," a White House statement said.
It added that Obama "believes that there are core interests at stake for the United States and that countries who violate international norms regarding chemical weapons need to be held accountable".
In remarks made on Friday morning, the US Defence Secretary, Chuck Hagel, said that his country would continue to seek "an international coalition" for strikes against Syria.
In a terse statement to parliament, Cameron said it was clear to him that the British people did not want to see military action.
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He conceded that "the British parliament, reflecting the views of the British people, does not want to see British military action".
The Prime Minister said while he believed in a "tough response" to the use of chemical weapons, he would respect, and not override, the will of the House of Commons.
Al Jazeera's James Bays, reporting from the UN headquarters in New York, said Cameron "is allowed under British law to ignore parliament".
"But that means if the British are to be involved in this they need another vote," he said.
At the start of the week, Cameron had seemed ready to join Washington in possible military action against Assad over the alleged chemical weapons attack.
But the push for strikes against the Syrian regime began to lose momentum as Britain's Labour Party announced its opposition to the move.
Cameron gave concessions, promising to give the UN inspectors time to report back to the UN Security Council and to do his outmost to secure a resolution there.
He also promised to give lawmakers a second vote in a bid to assuage fears that Britain was being rushed into an attack on Assad.
In the end, it was not enough to dispel lingering suspicions that what was billed as a limited campaign would turn into an Iraq-style quagmire.
Tony Travers, the director of the government department at the London School of Economics, said Cameron had clearly miscalculated when he brought parliament back early from its summer recess.
He said the move had been unpopular even within Cameron's Conservative Party.
"Clearly this will be seen as a defeat, it suggests he got the politics wrong, both with the opposition and with some members of his own party,'' Travers said.
"It's not great, it's not brilliant, nor is it the end of the world for him. He's lost votes before. It doesn't necessarily stop them taking further action, but they are going to have to start again really.''
He said there was "not a lot" of public support for British military activity in Syria.
Syria denies blame for the gas attacks and says they were perpetrated by rebels.
Washington and its allies say the denial is not credible.
On Thursday, the Syrian President said that his country would defend itself against any foreign military intervention, according to the state media.