The United States made it clear Thursday that it was ready to act alone to launch a punitive strike against Syria's chemical-armed regime, as top UN powers remained deadlocked.
Syrian strongman Bashar al-Assad vowed to resist any military intervention, and the governments of US allies Britain and France struggled to win domestic political backing for action.
Key US ally Britain had mounted an improbable bid to win UN backing for military action, but a meeting of the permanent Security Council members broke with no apparent breakthrough.
The 45-minute meeting was the second since Britain proposed a draft resolution to permit "all necessary measures" to protect Syrian civilians after a suspected chemical weapons attack last week.
But none of the envoys from Britain, China, France, Russia and the United States commented as they left, and the White House had already indicated that it was prepared to go it alone.
Earlier in the week reports had suggested that a Western strike was imminent, but questions have been raised about the quality of the intelligence linking Assad to the attack.
A strike could still go ahead, but the White House is reaching out to US lawmakers and has given its allies more time to placate domestic opposition and UN inspectors time to complete their mission.
"We certainly are interested in engaging with the global international community on this issue," White House spokesman Josh Earnest said.
"But at the same time, the president's chief accountability is to the American people that he was elected to protect.
"The president believes strongly in making the kinds of decisions and taking the kinds of steps that are necessary to protect our core national security interests that we've acknowledged are at stake in this situation."
President Barack Obama has said the alleged large-scale use of chemical weapons by Assad's regime is a threat to US security as well as a crime against the Syrian people.
US warships armed with scores of cruise missiles are converging on the eastern Mediterranean, and US military officials have said they are ready to launch a powerful barrage against regime targets in Syria.
Assad's ally Russia has blocked all attempts to toughen international sanctions against Damascus or authorize outside force to punish or unseat the regime.
Syria, meanwhile, is in the 29th month of a vicious civil war in which more than 100,000 people are credibly reported to have died.
As the stand-off continues, a team of UN inspectors are investigating reports -- believed by Western governments -- that last week's gas attack outside Damascus killed more than 350 people, including women and children.
A UN spokesman said Thursday that the team had collected "considerable" evidence and will brief UN secretary general Ban Ki-moon soon after they leave Syria on Saturday.
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"Starting tomorrow he will try to reach out to member states and take discussions forward on the question of what is happening in Syria," the spokesman said.
Ban has appealed for the inspectors to be allowed to complete their work before the major powers decide any follow-up action.
Assad remained defiant in the face of the Western threats.
"Syria will defend itself in the face of any aggression," state television cited him as telling a visiting delegation of Yemeni politicians.
He vowed that any attack would result in "victory" for the Syrian people.
His regime has denied using chemical weapons and blamed "terrorist" rebels.
The United States said it deployed a fifth destroyer to the eastern Mediterranean while Russia was reportedly sending in two warships and Britain dispatched fighter jets to Cyprus.
The mood among Damascus residents was fearful, while security forces prepared for possible air attacks by pulling back soldiers from potential targets and introducing tougher controls at roadblocks and hospitals.
Syria's nervous neighbors stepped up preparations for conflict, with Israel authorizing a partial call-up of army reservists while Turkey put its forces on heightened vigilance.
Obama, who a year ago warned that the use of chemical arms would cross a "red line," said Wednesday that Washington had definitively concluded that the Assad regime was to blame for the August 21 attack.
Asked how close he was to ordering a US strike Obama said: "I have not made a decision."
He said US action would be designed to send a "shot across the bow" to convince Syria it had "better not do it again."
France's President Francois Hollande met in Paris with one of the leaders of the rebel movements arrayed against Assad's rule, and vowed to maintain support.
British Prime Minister David Cameron told his parliament that he was convinced the Syrian regime was behind a chemical weapons attack, but admitted there was no "100-percent certainty."
"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," he said.
"It's about the large-scale use of chemical weapons and our response to a war crime -- nothing else."