Military intervention in Syria would hurt the global economy and push up oil prices. (AFP)
This reinforces Russian president Vladimir Putin's attempts to talk United States President Barack Obama out of air strikes.
The rift over Syria could overshadow a summit of the Group of 20 (G20) developed and developing economies taking place in St Petersburg, Russia, at which global leaders want to forge a united front on growth, trade, banking transparency and fighting tax evasion.
The club that accounts for two-thirds of the world's population and 90% of its output is divided over issues such as turmoil in emerging markets and the US Federal Reserve's decision to end its programme of stimulus for the US economy.
But no rift is wider than the one between the US and Russian leaders on possible military intervention in Syria to punish President Bashar al-Assad over a chemical-weapons attack that killed hundreds of people on August 21.
Putin was isolated on Syria at a Group of Eight meeting in June, the last big meeting of world powers, but now has China to back him at the G20 summit.
"Military action would have a negative impact on the global economy, especially on the oil price," Reuters quoted Chinese Vice-Minister of Finance Zhu Guangyao as telling a briefing before the start of the G20 leaders' talks.
In Beijing, foreign ministry spokesperson Hong Lei reiterated that any party that resorted to chemical warfare should accept responsibility for it, but said unilateral military action violated international law and would complicate the conflict.
Like Moscow, one of Syria's main arms suppliers, Beijing has veto powers on the United Nations Security Council. Obama is unlikely to win Security Council approval for military action, but is seeking the approval of the US Senate and Congress.
On Wednesday, the US Senate foreign relations committee voted in favour of military authorisation.
The influential committee voted by 10 votes to seven in favour of granting the formal military authorisation requested by Obama, paving the way for a full vote on the floor of the Senate early next week. But the committee also voted to accept controversial amendments proposed by hawkish Republican senator John McCain that would explicitly make it a policy of the US to seek to "change the momentum of the battlefield" in ways that would force Assad to negotiate his resignation.
"It is the policy of the United States to change the momentum on the battlefield in Syria so as to create favourable conditions for a negotiated settlement that ends the conflict and leads to a democratic government in Syria," said the second of two amendments proposed by McCain and Democrat Chris Coons.
France echoed Obama's call for action over the gas attack, which Washington blames on Syrian government troops and Moscow says may have been carried out by rebels trying to oust Assad.
"The position of France is to punish and negotiate," Foreign Minister Laurent Fabius told France 2 television before travelling to St Petersburg, where Putin is hosting the summit in a tsarist palace on the coast. "We are convinced that if there is no punishment for Mr Assad, there will be no negotiation," he said. "But obviously, it will be difficult."
Putin has said he would like to hold one-on-one talks with Obama, but a Kremlin spokesperson said no such meeting was planned. – Reuters, © Guardian News & Media 2013