A spokesman for Russian President Vladimir Putin says Russia would consider sending troops to fight in Syria if Damascus were to ask for it.

Russia on Thursday urged the United States and its allies to engage the Syrian government as a "partner" in the fight against the Islamic State group amid concerns over an ongoing Russian military buildup there.

Syrian Foreign Minister Walid al-Moallem denied reports on Thursday that Russian combat troops were fighting in Syria but said Syria would not hesitate to ask for Russia's help if needed.

Dmitry Peskov in comments to Russian news agencies on Friday said if such a request is made, it will be "discussed and considered," but he insisted the question is purely hypothetical at this stage.