The United States has signalled it could take unilateral action against Syria after last week's suspected chemical weapons attack.
Secretary of State John Kerry briefed members of Congress shortly after British MPs voted against British involvement in any American-led attacks. Mr Kerry says the US isn't bound by other countries' foreign policy decisions.
After the vote in London, Prime Minister David Cameron said the government would act accordingly", effectively ruling out British involvement in any strikes against Damascus.
The White House said it would "continue to consult" with London.
"President Obama's decision-making will be guided by what is in the best interests of the United States," a statement said.
The statement added that Mr 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".
The BBC reports administration officials on Thursday told a group of lawmakers in a conference call that "it is beyond a doubt that chemical weapons were used, and used intentionally by the Assad regime".
Congressman Eliot Engel, the senior Democratic member on the House Foreign Affairs Committee, said the officials cited evidence including "intercepted communications from high-level Syrian officials".
A British government motion was defeated by 285 to 272, a majority of 13 votes, on Thursday. Thirty Conservative and nine Liberal Democrat MPs voted against the motion.
Mr Cameron said it was clear Parliament did not want action and "the government will act accordingly".
A Labour amendment calling for "compelling" evidence, was defeated by 114 votes.
Earlier Mr Cameron conceded intelligence that the Syrian regime had used chemical weapons is not 100% certain.
He told an emergency debate in parliament that British intelligence chiefs believed it highly likely the Syrian government was responsible for an incident on 21 August in Damascus, in which at least 355 people died.
The government said it had legal advice that Britain could launch strikes against Syria without the backing of the United Nations.
The advice said action would be a legal "humanitarian intervention" - even if it was vetoed at the UN.
The prime minister's office said in a statement that Britain could still take "exceptional measures including targeted military intervention" on humanitarian grounds, even if the Security Council could not agree.
Opening the debate, Mr Cameron said: "It's not about taking sides in the conflict, it's not about invading, it's not about regime change or indeed working more closely with the opposition. "It's about the large-scale use of chemical weapons and our response to a war crime - nothing else.
"I am deeply mindful of the lessons of previous conflicts, and in particular the deep concerns in the country caused by what went wrong with the Iraq conflict in 2003," Mr Cameron said.
"One thing is indisputable: the well of public opinion was well and truly poisoned by the Iraq episode and we need to understand the public scepticism."
Opposition leader Ed Miliband said Labour was not ruling out military intervention but insisted there had to be a clear road-map to a decision.
"I do not rule out supporting the prime minister," Mr Miliband said. "But I believe he has to make a better case than he did today on this question."
Security Council members meet again
The five permanent members of the United Nations Security Council have held more talks on the Syria crisis on UN action.
The 45-minute meeting was the second since Britain proposed a draft Security Council resolution that would allow "all necessary measures" to protect civilians.
None of the envoys from Britain, China, France, Russia and the United States commented as they left the meeting in New York.
An inconclusive meeting was held on Wednesday on a draft resolution that would authorise "all necessary force" in response to an incident.
Russia and China have already vetoed three resolutions condemning President Bashar al-Assad, who the United States and Britain say used chemical weapons on his own people in Damascus.
The BBC reports Russia has close ties with the Assad government, supplying its armed forces with weapons and housing its warships in Syria's ports.
Earlier, German Chancellor Angela Merkel spoke to President Vladimir Putin over the phone to urge Russia to help the Security Council frame a "quick, unanimous international reaction".
UN Secretary General Ban Ki-moon has appealed for Western powers to await the findings of UN inspectors in Damascus. They will leave Syria by Saturday and report to him immediately.
If confirmed, the incident will be the deadliest use of chemical weapons since Saddam Hussein gassed Iraqi Kurds in 1988.
Mr Assad has told a group of Yemeni MPs that Syria would defend itself against any aggression. According to the Sana news agency, he said: "Syria, with its steadfast people and brave army, will continue eliminating terrorism, which is utilised by Israel and Western countries to serve their interests in fragmenting the region."
RAF jets sent to Cyprus
Britain has sent six RAF Typhoon jets to a base in Cyprus in a move to protect British interests as tensions grow.
The Ministry of Defence said the jets would not take part in any direct military action.
The MoD said it was purely a precautionary measure to ensure the protection of British interests at a time of heightened tension in the wider region.
Meanwhile, the BBC reports a state newspaper in China has warned there are no excuses for air strikes on Syria.
In Syria, information minister, Omran Ahmed Zoabi said the United States would be making a big mistake if it went ahead with a military strike.
He said the US did not have a convincing argument to wage war on Syria.