Moscow on Monday dismissed US concern of a Russian military buildup in Syria, saying its military aid to Bashar al-Assad was nothing out of the ordinary.

Over the weekend US Secretary of State John Kerry phoned his Russian counterpart Sergei Lavrov to express concern about reports of an "enhanced Russian buildup" in Syria.

"The Russian side has never concealed the fact that it is sending military equipment to the Syrian authorities to help them fight terrorism," Russian foreign ministry spokeswoman Maria Zakharova told AFP, commenting on the Kerry-Lavrov phone talks.

"Lavrov confirmed that such aid has always been provided and is being provided."

Citing US administration officials, The New York Times reported last week that Russia had sent a military advance team to its ally Syria and was taking other steps that Washington fears may signal plans to vastly expand military support for the beleaguered Assad.

Zakharova said she was not aware of the alleged Russian military build-up in Syria.

President Vladimir Putin said Friday it was premature to talk about Russia taking part in military operations against the Islamic State jihadist group.

A prominent Russian blogger suggested over the weekend that Moscow was apparently building up its military presence in Syria to help prop up Assad.

The blogger Ruslan Leviyev -- known for his investigations into Russian military activity in Ukraine -- referred to widely-circulated footage from Syria apparently showing a Russian-made BTR-82A armoured personnel carrier as well as reports on social networks that Russian paratroopers have been dispatched to Syria.

Moscow has denied sending regular troops to prop up separatist rebels in Ukraine, leaving activists and journalists to trawl through social networks for evidence of the Russian military presence abroad.

Liberal lawmaker Dmitry Gudkov on Monday said he sent a formal enquiry to Defence Minister Sergei Shoigu, asking whether Russian troops are fighting in Syria, and if so, whether any have died or been wounded.

"I'm doubtful that the Sunnis, the Shias and Alawites of the Middle East should be dearer to Russia than its own citizens," he wrote on Facebook.