Russia's Foreign Minister says his country is ready to support the Free Syrian Army (FSA) with air strikes and cooperate closely with the US in fighting the Islamic State of Iraq and the Levant (ISIL) group and other factions.
Sergey Lavrov's offer on Saturday was immediately rejected by Syrian rebel factions, which dismissed the idea they could cooperate with Russia while it supported President Bashar al-Assad.
"Russia is bombing the Free Syrian Army and now it wants to cooperate with us while it remains committed to Assad? We don't understand Russia at all," said Lieutenant Colonel Ahmad Saoud, a spokesman for the Division 13 rebel group, according to the AFP news agency.
Russia launched an air campaign in late September ostensibly against ISIL and other "terrorist" groups, but the FSA say most of the air strikes are targeting them and other moderate opposition groups.
Samir Nashar, a member of the Syrian National Coalition, the opposition's main political body, said "80 percent" of strikes had hit the FSA.
"Instead of talking about their willingness to support the Free Syrian Army, they should stop bombing it," he said.
The offer of air strikes in support of the FSA came as Lavrov and US Secretary of State John Kerry spoke on about organising talks between the Syrian government and the opposition.
In a telephone conversation held at the request of the US side, the Russian foreign ministry said on its website that the two men had also discussed tapping the potential of other countries in the region to push the political process forward.
Lavrov also spoke to his Iranian counterpart Mohammad Javad Zarif about the need to strengthen their cooperation in order to bring stability and security to the Middle East.
Russia wants Egypt and Iran to play a role in bringing a solution to the conflict in Syria, which has raged on since 2011.