Russia on Thursday accused Washington of "coordinating" deliveries of arms to Syrian rebels, despite assurances by the State Department that the United States provides no lethal assistance.

"Washington is aware of the deliveries of various weapons to illegal armed groups active in Syria. Moreover, judging by the declarations of US officials published in US media, the US coordinates and provides logistical assistance in such deliveries," the foreign ministry said in a statement.

Russia's top general Nikolai Makarov on Wednesday said rebels fighting against Bashar al-Assad's army in Syria are using US-made Stingers, a type of shoulder-launched missile systems also known as MANPADs.

State Department spokeswoman Victoria Nuland promptly denied that the US is delivering any such, or any other, weapons to the rebels.

"We are providing no lethal assistance to the Syrians," she said, adding that the only MANPADs sighted by the US in Syria were "Soviet vintage".

In its statement, the Russian foreign ministry acknowledged that "the US does not deliver MANPADs to the rebels" directly, and did not specify how the alleged logistical assistance is carried out.

Makarov said Russia did not yet know who was bringing the Stingers into Syria, adding it was possible that these and other weapons could have been delivered from abroad on several means of transport, including passenger planes.

"For this, all kinds of transport could be activated, including civil aviation. This is a serious matter," he said.

Russia is under sustained pressure from the West, Turkey and Assad's foes in the Arab world to cut its military cooperation with the Syrian regime.

President Vladimir Putin last week defended Russia's right to trade weapons with whoever it wanted, so long as sales did not break any sanctions from the UN Security Council where Moscow has a permanent, veto-wielding seat.

"In all other cases, no one can on any pretext dictate to Russia or any other state with whom and how it should trade," Putin said.

Moscow has refused to take sides against Assad, condemning the West and Turkey for making clear their support for the rebels battling his regime.