US president Barack Obama has lifted the threat of immediate punitive air strikes on Syria, even as the regime in Damascus said it was primed for any assault.
Taking a huge political gamble, Mr Obama on Saturday asked Congress to authorise military action against Syria to punish an alleged chemical weapons attack on a Syrian suburb that killed more than 1,400 people.
In doing so, he risks suffering the same fate as British prime minister David Cameron, who on Friday lost his own vote on authorising military action in parliament.
The Republican-controlled House of Representatives contains conservatives who revile the president and have obstructed his agenda across the board.
- Obama asks Congress to approve Syria strike
- Secretary of state Kerry speaks with Syrian opposition
- White House believes Congress will vote in favour of a military strike
- UN findings on chemical weapons use may take three weeks
- Syria keeping its 'finger on the trigger'
However, Mr Obama says he believes it is important to secure support from Congress to wage war, and the US Constitution states that Congress - and not the president - has the power to declare war.
House speaker John Boehner said that the chamber would debate Syria as soon as it comes back into session on September 9, meaning that politicians will not be called back early from their summer break.
Mr Obama says he will also discuss the US case for action on Syria with world leaders at the G20 Summit meeting in Russia next week.
The president, however, maintains that military force should be the price for what the US says is the "undeniable" use of chemical weapons by Syria, namely in a poison gas attack in the suburbs of Damascus on August 21 that it says killed 1,429 people, including at least 426 children.
"Our military has positioned assets in the region," Mr Obama said.
"We are prepared to strike whenever we choose."
Senior administration says the White House believes Congress will vote in favour of a military strike.
However, Republican senators John McCain and Lindsey Graham said they could not support isolated military strikes on Syria that are not part of a bigger strategy.
"We cannot in good conscience support isolated military strikes in Syria that are not part of an overall strategy that can change the momentum on the battlefield, achieve the president's stated goal of [Syrian president Bashar al-] Assad's removal from power, and bring an end to this conflict, which is a growing threat to our national security interests," they said in a statement.
Meanwhile, US secretary of state John Kerry spoke to the Syrian opposition leader on Saturday to underscore the determination of the US to hold the Syrian government accountable, a State Department official said.
Mr Kerry spoke with Syrian opposition coalition president Ahmed Assi al-Jarba to underscore Mr Obama's "commitment to holding the Assad regime accountable for its chemical weapons attack against its own people on August 21st," the official said.
Mr Kerry also spoke with the foreign ministers of Saudi Arabia and Japan about Syria.
Syria has its 'finger on the trigger'
Syria, meanwhile, said it has its "finger on the trigger" as it braced for what it had considered an imminent Western military strike, following the departure of UN weapons inspectors.
"The Syrian army is fully ready, its finger on the trigger to face any challenge or scenario that they want to carry out," prime minister Wael al-Halqi said.
In Damascus, the mood was heavy with fear, and security forces were making preparations for possible air strikes, pulling soldiers back from potential targets.
Residents were seen stocking up with fuel for generators in case utilities are knocked out by a strike.
Meanwhile, neighbouring Iran warned that any strike would trigger reactions beyond the borders of Tehran's key regional ally.
"The fact that the Americans believe that military intervention will be limited to within Syrian borders is an illusion," said commander Mohammad Ali Jafari, the head of Iran's elite Revolutionary Guards.
UN findings may take three weeks
United Nations spokesman Martin Nesirky said inspectors who spent four days investigating the alleged chemical attack last week would not issue a report on their findings until laboratory tests are conducted and a full assessment made, which could take up to three weeks.
The team of inspectors, which included nine experts from the Organisation for the Prohibition of Chemical Weapons (OPCW) and three from the World Health Organisation, arrived at the OPCW's headquarters at The Hague on Saturday evening after leaving Syria early in the morning.
They are due to report straight back to UN chief Ban Ki-moon and detail their conclusions on whether a poison gas attack actually did take place in Damascus suburbs on August 21.
"The evidence collected by the team will now undergo laboratory analysis and technical evaluation according to the established and recognised procedures and standards," the OPCW said in a statement. "These procedures may take up to three weeks."
Russia scoffs at US claims over chemical attack
The Obama administration's claims that it already had firm evidence that Assad's regime launched the chemical attack brought a contemptuous response from Russian president Vladimir Putin, whose country is a close ally of Syria, saying claims the regime had used chemical weapons were "utter nonsense" and demanding proof.
The US president has said he is looking at a "wide range of options" but has ruled out "boots on the ground" or a "long-term campaign."
"We are looking at the possibility of a limited, narrow act," Mr Obama said on Friday.
Syria has denied responsibility for the alleged incident and has pointed the finger of blame at "terrorists" - its term for rebels ranged against Mr Assad's forces.
Mr Cameron said on Saturday he supported Barack Obama's position after the US president said he would seek a congressional vote for military action.
British PM supports Obama's position on Syria
Mr Cameron's plans for Britain to join a potential military strike were thwarted on Thursday night when parliament narrowly voted against a government motion to authorise action against Syria in principle.
"I understand and support Barack Obama's position on Syria," Mr Cameron said on his official Twitter feed.
Mr Cameron's defeat called into question Britain's traditional role as the US' most reliable military ally, a role Mr Cameron has worked hard to cement.
British defence secretary Philip Hammond later said he thought the United States would be disappointed that Britain "will not be involved".
Earlier on Saturday, hundreds of anti-war protesters rallied in London's Trafalgar Square to proclaim "victory" after Thursday's parliamentary vote and demand no military intervention from other states.
Meanwhile, French president Francois Hollande reaffirmed to Mr Obama in a telephone call on Saturday his will to sanction Syria.
More on the crisis in Syria