World leaders from G20 are meeting in St Petersburg, Russia, amid sharp differences over possible US military action against Syria, in response to what the US administration calls a deadly chemical weapons attack by the Syrian government.
Thursday's summit came hours after a US Senate panel voted to give President Barack Obama authority to use military force against Syria - the first time lawmakers in that country have voted to allow military action since the October 2002 votes authorising the invasion of Iraq.
The US and Russia, which is a key Syrian ally, remain at odds as Obama has tried to build his case for military action.
The US president has vowed to continue to try to persuade his Russian counterpart, Vladimir Putin, of the need for punitive strikes against President Bashar al-Assad for using chemical weapons when the two meet at the summit.
As Putin opened the summit, he spoke exclusively about the global economic crisis, which forms the primary agenda of the summit, stressing the need for co-ordinated international policy making in order to combat continuing volatility in economic markets.
He suggested that world leaders discuss the subject of Syria during an official dinner on Thursday night, so as not to take away from the summit's primary economic agenda.
Kerry 'a liar'
Earlier, Putin had again questioned Western evidence justifying a military strike against Syria, accusing US Secretary of State John Kerry outright of lying when, in urging Congress to approve strikes, he played down the role of al-Qaeda in the rebel forces.
"Al-Qaeda units are the main military echelon, and they know this," Putin said. "He is lying and knows he is lying. It's sad."
Putin said that the US Congressional approval without a UN Security Council resolution would be an act of aggression. He also told The Associated Press this week that he "does not exclude" supporting UN action - if it is proven that the Syrian government used poison gas on its own people.
Obama had previously stated that he was prepared to bypass the UN Security Council on the issue, but had put the matter to a Congressional vote. Members of the full US Senate are due to debate the matter next week.
On Thursday, following initial discussions at the G20 summit, the UK Prime Minister, David Cameron, said that his country had received new evidence that sarin gas had been used against civilians by the Syrian government.
The German Foreign Minister, Guido Westerwelle, said on Thursday that the International Criminal Court should be mandated to examine the alleged use of chemical weapons in Syria.
The UN Secretary-General, Ban Ki-moon, briefed G20 summit delegates on Thursday on the UN chemical weapons inspectors' trip to Syria, while stressing that "providing more arms to either side is not the answer".
"There is no military solution," Ban said.
The conflict in Syria, which began with a popular uprising in March 2011, has been stalemated, and it is not clear if the US military strikes over the alleged chemical attack would change that. Obama has said he has been seeking limited pinpoint action to deter future chemical attacks, not regime change.
Economic and nuclear risks
Meanwhile, China warned other world powers of global economic risks following potential US strikes.
Speaking in St Petersburg ahead of the G20 summit on Thursday, Chinese Vice Finance Minister Zhu Guangyao said such "military action would definitely have a negative impact on the global economy, especially on the oil price".
He urged a negotiated UN solution to the standoff over allegations that Syria's government used chemical weapons against its own people.
Russia has also issued a warning that US strikes on Syria's atomic facilities might result in a nuclear catastrophe and is urging the UN to present a risk analysis of such a scenario. The issue will be brought up at a meeting of the 35-nation IAEA board next week, the Interfax news agency reported.
Little international support
Obama has been lobbying for international and domestic support for punishing Assad's regime, which the US says fired rockets loaded with the nerve agent sarin on rebel-held areas near Damascus before dawn on August 21, killing hundreds of civilians.
In-depth coverage of escalating violence across Syria
So far, however, he has won little international backing for action. The US has France's support for military action in Syria, but several other G20 powers, including China and Germany, have firmly voiced their
Ben Rhodes, a senior Obama national security aide, said that the US would use the summit in St Petersburg to "explain our current thinking" to allies and partners and explore what type of "political and diplomatic support they may express for our efforts to hold Syrian regime accountable".
With pressure mounting on the G20 to make a decision regarding the conflict, the UN announced on Thursday that Lakhdar Brahimi, its special envoy to Syria, was travelling to St Petersburg to make a push for peace talks.
Walid Muallem, the Syrian foreign minister, is due in Moscow on Monday, after the summit has ended, for talks with his Russian counterpart, Sergei Lavrov.