Air strikes by the Russian military in support of forces loyal to President Bashar al-Assad have helped turn the tide in Syria, Russian Foreign Minister Sergei Lavrov said Tuesday.

Lavrov said that the Russian air force's strikes had "really helped to turn around the situation in the country, helped towards reducing the territory controlled by terrorists" since Moscow launched a bombing campaign at Assad's request on September 30.

Russia's top diplomat also denied reports that Russia had asked long-time ally Assad to step down and offered him political asylum.

"This is not true," Lavrov said of media reports that Russia's late military intelligence chief Igor Sergun had travelled to Syria to ask Assad to resign. "No one asked for political asylum and no one offered anything of the kind."

Russia has staunchly supported Assad's beleaguered regime and said that his removal could not be a prerequisite for a deal to end the conflict, which has left more than 260,000 people dead and millions displaced.

The West has accused Russia -- whose jets carried out more than 5,000 combat sorties in Syria last year -- of mainly targeting moderate rebels fighting the Assad regime as well as inflicting civilian casualties.

Moscow meanwhile insists it is tackling "terrorist" groups such as Islamic State.

Forces backing Assad have recently made several key gains on the ground.

Regime forces backed up by several dozen Russian air strikes overnight captured the rebel stronghold of Sheikh Miskeen close to the border with Jordan, the British-based monitor Syrian Observatory for Human Rights said Tuesday.

Russian planes from Friday to Sunday carried out 169 flights, bombing almost 500 targets, the Russian defence ministry said Monday.

Talks aiming to end the brutal war that has lasted almost five years are set to begin in Geneva on Friday after delays due to disagreements over who would represent the splintered opposition, United Nations envoy Staffan de Mistura told reporters.