The rift over Syria could overshadow a summit of the Group of 20 (G20) developed and developing economies in St. Petersburg 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 percent of its output is divided over issues such as turmoil in emerging markets and the Federal Reserve's decision to end its program 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 based on conflicting reports of an alleged chemical attack on August 21 near Syrian capital.

"Military action would have a negative impact on the global economy, especially on the oil price - it will cause a hike in the oil price," Chinese Vice Finance Minister Zhu Guangyao told a briefing before the start of the G20 leaders' talks.

In Beijing, Foreign Ministry spokesman Hong Lei reiterated that any party resorting to chemical warfare should accept responsibility for it but said unilateral military actions violate international law and would complicate the conflict.

US President Barack Obama is unlikely to win Security Council approval for military action but it has turned to the US Congress to have more parties engaged in his controversial decision.

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 militants trying to oust Assad.

Putin has said he would like to hold one-on-one talks with Obama but a Kremlin spokesman said no such meeting was planned.

Obama has also been criticized by Kremlin for undermining efforts for bringing the two sides of the Syrian conflict to the negotiation table by moving its warships toward Syria and calling for military actions instead of political solutions.

Foreign ministers from key states in the G20 - which includes all five permanent UN Security Council members - will also discuss Syria on the sidelines of the meeting.

Any G20 decision on Syria would not be binding but Putin would like to see a consensus to avert military action for humanitarian reasons.

The war in Syria has already left more than 100,000 people dead, according to UN figures.

A US attack is expected to prolong the war and cause more deaths.

SHI/SHI