Following a 285-272 vote against a motion by British Prime Minister David Cameron to authorise a military response in principle, British Defense Secretary Philip Hammond confirmed Britain would not be involved in any action against Syria.
Hammond said key ally Washington would be disappointed that Britain "will not be involved," although adding, "I don't expect that the lack of British participation will stop any action.
But he told BBC TV, "It's certainly going to place some strain on the special relationship," referring to ties with Washington.
US officials suggested President Barack Obama would be willing to proceed with limited actions against Syria even without specific promises of allied support because US national security interests are at stake.
"President Obama's decision-making will be guided by what is in the best interests of the United States," White House spokeswoman Caitlin Hayden said in a statement after the British vote. "He 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."
US Defense Secretary Chuck Hagel said Washington would continue seeking out an international coalition to act together on Syria.
In a briefing with senior lawmakers on Thursday, Obama administration officials said they had "no doubt" chemical weapons were used in Syria and that Syrian President Bashar al-Assad's government had used them, US Representative Eliot Engel, who participated in the call, told Reuters.
Britain's Cameron, saying he would not override the will of parliament, said it was clear that lawmakers did not want to see a military strike on the Syrian government to punish it for a chemical weapons attack in the suburbs of Damascus last week.
Asked by Labour leader Ed Miliband whether he would promise not to circumvent parliament and authorize military action, 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."
The parliamentary vote reflected deep misgivings stemming from Britain's involvement in the 2003 invasion of Iraq.
Proof of chemical attack
The United States and its allies have "no smoking gun" proving Assad personally ordered the attack on a rebel-held Damascus neighborhood in which hundreds of people were killed, US national security officials said.
Syria denies blame for the gas attacks and says they were perpetrated by rebels. Washington and its allies say the denial is not credible.
UN expert to report back next week
While UN chemical weapons inspectors spent a third day combing the rebel-held area where the attack took place, traffic moved normally elsewhere in Damascus, with some extra army presence but little indication of any high alert
The team of inspectors would leave Syria on Saturday and report to Secretary-General Ban Ki-moon.
France and Germany urged the world body to pass its report on to the decision-making Security Council as soon as possible "so that it can fulfill its responsibility with regards to this monstrous crime."
Expectations of imminent turmoil eased as the diplomatic process was seen playing out into next week, and the White House emphasized that any action would be "very discrete and limited," and in no way comparable to the Iraq war.
The United States, Britain and France have said action could be taken with or without a Security Council resolution, which would likely be vetoed by Russia, a close ally of Assad. But some countries are more cautious: Italy said it would not join any military operation without Security Council authorization.
