President Obama and his top aides tried to rally support Thursday for retaliatory strikes in Syria, saying they remain convinced that the Assad regime used chemical weapons, but hopes for an international coalition took a major hit when the British Parliament voted against military action.
British lawmakers questioned the strength of the claims that forces loyal to President Bashar Assad used poison gas to attack rebels in a Damascus suburb last week — a skepticism that U.S. lawmakers share, amid reports that U.S. intelligence officials are uncertain who controls Syria’s stockpiles of poison gas.
Senior officials said Mr. Obama is still considering unilateral action without his British allies, arguing that core U.S. national security interests are at stake. The White House steadfastly stood by Mr. Obama’s claim that Syria attacked its own citizens with chemical weapons, saying the evidence is “very convincing.”
“There is a preponderance of evidence,” White House spokesman Josh Earnest told reporters, though he said the administration isn’t ready to make public an unclassified report detailing that evidence.
Late Thursday, the administration held a 90-minute conference call with 26 high-ranking members of Congress, who are on a five-week summer recess.
Rep. Eliot L. Engel of New York, the senior Democrat on the House Foreign Affairs Committee, said the administration told them that Mr. Obama was “still weighing his options and will continue to consult with Congress.”
Sen. James M. Inhofe, Oklahoma Republican, said administration officials set out a only “broad range of options” with no timetable, and Rep. Howard P. “Buck” McKeon, California Republican, said the administration is still in the process of declassifying evidence on the use of chemical weapons.
All those reactions stand in contrast to speculation earlier in the week that this briefing would be a semi-official notification that strikes on Syria would soon commence.
The briefing came hours after a more open debate at the British House of Commons, which Prime Minister David Cameron called back into session this week to debate military action in Syria. Mr. Cameron had hoped for approval, but members of Parliament rejected his overtures on a 285-272 vote.
“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,” Mr. Cameron said afterward. “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.”
The Obama administration said after the vote in Parliament that the U.S. is willing to act alone against Syria.
“We have seen the result of the Parliament vote in the U.K. tonight,” National Security Council spokeswoman Caitlin Hayden said in a statement. “The U.S. will continue to consult with the U.K. government — one of our closest allies and friends.
“As we’ve said, President Obama’s decision-making will be guided by what is in the best interests of the United States,” she said. “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.”
Still, the defeat further isolates Mr. Obama, who has decided against pushing for a vote at the United Nations to approve military action, citing Russia’s opposition.
After signaling that it hoped for quick action, the White House appeared to back away from a timetable. Mr. Earnest said the phone briefing for Congress was just the latest and that “there will be additional consultations tomorrow and in the days and weeks ahead.”
They are finding an increasingly skeptical audience on Capitol Hill.
As of Thursday, 185 members of the U.S. House had signed on to letters demanding that the president come to Congress with a full case for military action.
One of those letters, signed by 140 lawmakers, mostly Republicans, said the president had a duty to consult. The other letter, signed by Democrats, said he must obtain permission from Congress first.
“While the ongoing human rights violations and continued loss of life are horrible, they should not draw us into an unwise war — especially without adhering to our own constitutional requirements,” the Democrats said in their letter.
A HuffingtonPost/YouGov poll taken this week found little support for military action: Just a quarter of adults surveyed said the U.S. should launch airstrikes to aid the rebels. Another 41 percent were opposed, and 34 percent were unsure.
A majority of those surveyed, however, do believe Syrian troops used chemical weapons against the rebels.
The congressional Democrats’ letter urged Mr. Obama to let the U.N. inspectors finish their work and told the president to continue pushing for U.N. approval of any further action.
The Obama administration, though, has ruled out that option, saying Russia’s opposition — the Kremlin holds a veto at the Security Council, which would have to approve any authorization to use force — is too big of a hurdle.
U.N. Secretary General Ban Ki-moon has pleaded with Western nations to let U.N. weapons inspectors in Syria finish their work. The inspectors are investigating various sites where rebels say chemical weapons attacks took place, including in the Damascus suburbs where troops loyal to Mr. Assad shelled rebels and civilians last week.
Reports say hundreds were killed in the attack, and photos and video afterward showed dead children, covered in white shrouds, lined up shoulder to shoulder, without any visible evidence of trauma. The U.N. inspectors are expected to finish their work by the end of the week.
Syria and its ally Russia have suggested that it was rebels who deployed chemical weapons.
The Associated Press, citing two unidentified intelligence officials and two other government sources, reported Thursday that the evidence linking the Assad regime to the chemical weapons strike is not a “slam dunk.”
The anonymous officials said a report by the Office of the Director for National Intelligence has key caveats — including an acknowledgment that the U.S. intelligence community no longer has the certainty it did six months ago of where the regime’s chemical weapons are stored, nor does it have proof that Mr. Assad ordered a chemical weapons attack.
Confronted with that report, the White House spokesman discounted the wire service’s use of anonymous sources and said he places more credibility in the assessments of the president, Vice President Joseph R. Biden and others who were willing to go on the record.
“I have on-the-record statements from the president of the United States, the vice president, the secretary of state,” Mr. Earnest said. “I’ve got on-the-record statements from the prime minister of the United Kingdom. We’ve got the president of France. So I leave it to you to decide whether or not you believe anonymous [sources] that are included in the AP story, or an on-the-record statement from people who have looked at exactly the same information.”
Questions about the quality of intelligence also plagued Mr. Cameron in the British debate.
Mr. Cameron told the House of Commons that he is aware the debate has been “poisoned by the Iraq episode,” where the U.S. made the case that it needed to go to war to oust Saddam Hussein because his regime had weapons of mass destruction. However, no stockpiles were found.
“This is not like Iraq,” Mr. Cameron said. “What we are seeing in Syria is fundamentally different. We are not invading a country. We are not searching for chemical or biological weapons.”
• Stephen Dinan and Guy Taylor contributed to this report.