David Cameron has lost the parliamentary vote seeking Britain joining a US-led strike on strife-torn Syria. Amid the looming military intervention against President Bashar al-Assad's regime, the coalition was defeated by 285 to 272.
The prime minister asserted that the UK will "act accordingly" following the rejection of military strike.
When pressed whether Britain will approve military action through other ways, Cameron said: "I can give that assurance. I strongly believe in the need for a tough response to the use of chemical weapons, but I also believe in respecting the will of this House of Commons."
He added: "It is very clear tonight that while the House has not passed a motion, it is clear to me that the British parliament, reflecting the views of the British people, does not want to see British military action - I get that and the government will act accordingly."
However, it is widely believed that Cameron is disappointed by the unexpected rejection and the parliament defeat is seen as an acute embarrassment for the coalition.
Hailing the MPs' decision, Labour leader Ed Miliband said the rejection is a response to Cameron's "cavalier and reckless leadership".
Conservative MP Adam Holloway told Sky News: "To me what matters here is not so much the arithmetic of the vote but that it is much less likely now that we won't be intervening in a horrible civil war that is fast becoming a regional conflict. Outrage isn't a strategy."
A stunned US said it would "continue to consult" with the UK as it is "one of our closest allies".
The White House said in a statement: "President Obama's decision-making will be guided by what is in the best interests of the United States."
The statement added that the US president "believes that there are core interests at stake for the United States and that countries that violate international norms regarding chemical weapons need to be held accountable".
The US authorities have been saying with certainty that the Assad regime had used chemical weapons, which the US had considered to be a "red line".
Fraser Nelson, the editor of right-wing The Spectator and a columnist for The Daily Telegraph, wrote: "David Cameron failed the test of trust, and paid the price. Parliament has rejected the PM's vision of this country's place in the world."
Labour blogger Sunny Hundal tweeted: "A sitting Prime Minister loses the support of his own party on a motion to go to war. There isn't a bigger humiliation, frankly.