Tensions were evident even before Obama's arrival in St Petersburg to lobby world leaders to support for a planned military strike against Syria as the Pentagon had to clarify Secretary of Defense Chuck Hagel's assertion that Russia provided chemical weapons to Syria. (Agencies)
Also, Russian President Vladimir Putin accused Secretary of State John Kerry of lying about al-Qaeda's links to Syrian rebels.
Obama is among the leaders who have now arrived at the G20, along with British Prime Minister David Cameron, Chinese President Xi Jinping and Prime Minister Manmohan Singh.
While Syria is not officially on the G20 agenda, leaders were expected to discuss it on the sidelines. The annual summit of the G20 group of developed and developing nations is supposed to concentrate on the global economy. The US has alleged that the nerve agent sarin was used by the Bashar al-Assad regime on August 21 and that at least 1,429 people were killed, including over 400 children, a charge denied by the Syrian government.
All five permanent members of the United Nations Security Council -- the US, Great Britain, France, China and Russia -- are attending the summit.
Putin has already warned that action without UN approval would be "an aggression". But Obama has said the credibility of the international community was on the line after Syria's use of chemical weapons which he described as "barbaric".
In a bid to help UN chief Ban Ki-moon's efforts to hasten a peace conference aimed at ending the conflict, UN-Arab League envoy on Syria Lakhdar Brahimi will attend the G20 summit.
"The Secretary General has just announced that the Joint Special Representative for Syria, Lakhdar Brahimi, is on his way to Russia to help him push, on margins of the G20 summit in Saint Petersburg, for the International Conference on Syria," the UN spokesperson said in a statement.
Meanwhile, the Senate Foreign Relations Committee, after more than 6 hours of deliberations spread over two days, voted 10-7 last night to approve the authorization resolution for military action against the Assad regime. The war resolution allows US a time frame of 60 days to achieve its objective to degrade chemical weapons capabilities of the Assad regime but prevents the use of troops on ground.
The full Senate is now expected to debate the measure and vote early next week.
In a statement, the White House commended for moving swiftly and for working across party lines on behalf of the national security, adding that the US is stronger when its President and Congress work together.
"The military action authorized in the resolution would uphold America's national security interests by degrading Assad's chemical weapons capability and deterring the future use of these weapons, even as we pursue a broader strategy of strengthening the opposition to hasten a political transition in Syria," the White House Press Secretary, Jay Carney, said.
The resolution is under consideration after last week Obama stepped back from a strike on Syria to first seek approval from Congress, which returns from recess next week.
Obama has exuded confidence that the Congress would authorize his request for a military strike against the Assad regime. "What happens if Congress doesn't approve it? I believe that Congress will approve it," Obama said yesterday.
"I believe Congress will approve it because I think America recognizes that, as difficult as it is to take any military action -- even one as limited as we're talking about -- even one without boots on the ground -- that's a sober decision," he said.
The US has also said it not only risks losing its international allies and friends, but also its credibility at the world stage if no military action is taken against the Assad regime for alleged use of chemical weapons.
"If we fail to act, we're going to have fewer allies. We are going to have fewer people that count on us, certainly in the region," Secretary of State John Kerry has told the US Senate.
Even as Russia and China oppose unilateral action outside UN's mandate, France has stood beside the US, calling for strong action against Syria.
France has vowed to "punish" Assad for the alleged attack and this week released an intelligence report that blamed for the assault on the Syrian leader's regime.
Iran has called allegations of the chemical weapons attack by the regime a "pretext" to launch strikes against the country. Iran has pledged support to Damascus "until the end".
The US and their allies "are using the chemical weapon as a pretext," and "are saying that they want to intervene for humanitarian reasons," Iran supreme leader Ayatollah Ali Khamenei said.
Tensions were evident even before Obama's arrival in St Petersburg to lobby world leaders to support for a planned military strike against Syria as the Pentagon had to clarify Secretary of Defense Chuck Hagel's assertion that Russia provided chemical weapons to Syria.