WASHINGTON, Aug 29: The United States appeared on Thursday to have backed down from an immediate punitive military action against Syria as British lawmakers demanded more evidence for supporting the strike.

During a parliamentary debate in London, MPs questioned the British government’s resolve to support a US military strike against Syria for allegedly using chemical weapons against its own citizens. They demanded more time and evidence for supporting any action against the Syrian government for the Aug 21 incident.

The debate had an immediate impact in the United States where House Speaker John Boehner sent a letter to President Barack Obama, demanding more information on the potential military strike.

Other lawmakers, from both Republican and Democratic parties, urged Mr Obama to take the US Congress into confidence before the action.

“The speaker made clear that before any action is taken, there must be meaningful consultation with members of Congress, as well as clearly defined objectives and a broader strategy to achieve stability,” Mr Boehner’s spokesman Brendan Buck said.

Faced with this unexpected development, the White House insisted that President Obama’s first consideration was protecting his country’s national security interests, although he was also seeking support of the international community on this issue.

“The US president is elected to protect the national security of the United States of America and … the decision he makes about our foreign policy is (based on) our national security interests,” said White House Principal Deputy Press Secretary Josh Earn.

In an interview to US Public Broadcasting Service on Wednesday afternoon, the president said it was in the US national security interest to punish Syria for using chemical weapons.

“If we are saying in a clear and decisive but very limited way, we send a shot across the bow saying, stop doing this, this can have a positive impact on our national security over the long term,” he said.

But US defence experts, in interviews to various television channels, said they believed the Obama administration may delay the military action until UN inspectors report back from Damascus.

The UN team will leave Syria on Saturday and then report to Secretary-General Ban Ki-moon.

Yet, at the White House briefing, Mr Earn warned that “there is a particular timeframe in which this decision has to be made” and a senior lawmaker noted that President Obama had the powers to order a military action without consulting Congress.

Senator Robert Menendez, who heads the Senate Foreign Relations Committee, said war powers gave the president the power to do so but he has to consult Congress within 60 days after the attack. “From my perspective, I think there is a compelling case to act, in a limited way,” he added.

He supported President Obama’s claim that a US intelligence assessment had “concluded that the Syrian government in fact carried these out”.

“There is a preponderance of publicly available evidence,” said Mr Earn when asked at the White House briefing if the Obama administration had more than circumstantial evidence.

Asked if the United States will go alone if the international community did not support its action against Syria, he said: “I do not want to pre-suppose a decision that has not been made yet.”

He insisted that US allies around the globe, including the Arab League, supported the US position.

The chemical attacks had happened “in a very volatile region and in the most volatile country” and the international community could not afford to let it go unnoticed, he said.

Mr Earn noted that the United States had a defence treaty with Turkey, had vowed to protect Israel and had a wide-ranging relationship with Jordan and that’s why it could not ignore Syria’s action.

Asked if the United States would wait for UN inspectors to submit their report before ordering a strike, the White House official said the inspectors had a limited mandate to determine if chemical weapons had been used, and not to determine who used them.

“The president demonstrated a clear willingness to consult and invest in the UN process,” he said. “Unfortunately what we are seeing right now is Russia repeatedly blocking efforts in the UN to hold Syria responsible.”

Meanwhile, France and Germany urged the UN to pass its report on to the Security Council as soon as possible.