Syria's foreign minister on Monday passed on the personal thanks of President Bashar al-Assad to Russian counterpart Vladimir Putin for his support, as he held talks in Moscow amid growing expectations of military action against the regime.

Foreign Minister Walid al-Muallem held talks with Russian counterpart Sergei Lavrov as US lawmakers were to return Monday from a summer break and debate whether to approve limited US military action in Syria.

"The president asked me to pass on his thanks to Putin for his position during and after the G20 summit" in Saint Petersburg last week, Muallem told Lavrov at the start of talks.

Lavrov assured Muallem that Moscow's position on Syria was "well known and not subject to changes".

"There is no alternative to a peaceful solution to the crisis in Syria" Lavrov said, rejecting any "military solution involving outside intervention".

Russia has vehemently opposed US-led strikes against the Assad regime, warning it could destabilise the whole Middle East, and Putin at the G20 has vowed to help Syria if it was hit.

Moscow has also made clear it is unconvinced the regime was behind a chemical weapons attack outside Damascus on August 21 that the United States and its allies say was carried out by the government and demands retribution.

Muallem told Lavrov that the US military intervention could destroy attempts to convene a peace conference in Geneva to end the bloodshed.

"Right up to now we are ready (to take part). But I do not know what could happen after an American aggression. It's possible the rockets will land and wreck this conference," he said.

His visit comes days after Putin refused to give ground on Russia's position over Syria in talks with world leaders at the G20 summit in Saint Petersburg.

Putin held an unscheduled meeting with US President Barack Obama but said afterwards that the two had failed to narrow their differences.

"He (Obama) disagrees with my arguments, I disagree with his arguments," Putin stated with characteristic bluntness.

Despite insistent Western pressure, Russia has refused to abandon its cooperation with the Assad regime throughout the two-and-a-half year conflict that has claimed more than 100,000 lives according to UN figures.

It has defiantly continued military cooperation, although Putin said last week Moscow had suspended deliveries of S-300 missile systems under a contract that outraged the West.

Russia's close ties to Damascus date back to the alliance between the Soviet Union and Bashar al-Assad's late father Hafez. The Kremlin fears losing arms contracts and influence if the dynasty falls.

Muallem last visited Moscow in February, when he vowed that the regime was ready for talks with anyone who favours dialogue, including armed rebels.

Russia and the United States agreed in May to organise the peace conference bringing all the sides to the negotiating table but the idea is far from materialising amid the tensions between Moscow and Washington.

The United States has indicated that it wants military action to punish the Assad regime for the suspected chemical attack. The strikes were delayed after Obama said he would first seek the approval of Congress.