German Chancellor Angela Merkel said Tuesday that she hoped an international consensus could still be reached at this week's G20 summit in response to an alleged chemical attack in Syria.

Merkel, who has repeatedly ruled out German participation in any US-led military strike against President Bashar al-Assad's regime, called for a fresh attempt to persuade summit host Russia to back unspecified consequences for Syria.

"We say clearly that Germany will not participate in military action (in Syria) but we add that we want to do everything possible in the remaining days to have a united response of the international community," she told deputies in a parliamentary debate ahead of a September 22 general election.

"I have to say that this is not very likely but the time should be used. And that is why we are in constant talks with all our international partners, with Russia. And that is why we want to use the G20 meeting to do everything in our power to reach a common position of the international community. I think this is in everyone's interest."

President Vladimir Putin of Russia, a vocal critic of the West's policies on Syria, has expressed strong doubt that Assad was behind an alleged chemical attack on 21 August  that has prompted the call for military action.

Russia has repeatedly blocked UN Security Council action against the Assad regime.

The Syrian crisis does not formally feature on the official agenda of the annual summit of the world's top 20 developed and emerging nations.

But there can be little doubt it will dominate bilateral meetings and may yet feature in plenary sessions of the two-day gathering in Saint Petersburg.

US President Barack Obama shocked Washington and the world on Saturday when he decided to seek support for military action in Syria from Congress, when it seemed US cruise missile strikes on Assad's forces and assets were imminent.

The move pushed back any potential strikes by several days.