Syrian rebels battling the regime of President Bashar al-Assad have shoulder-launched missile systems, including US-made Stingers, Russia's top general claimed Wednesday, prompting a strong denial from Washington.

Russian chief of staff General Nikolai Makarov, whose country is the Damascus regime's top arms supplier and has refused to back the opposition, said it was not clear who had delivered the weapons.

"We have information that the rebels fighting the Syrian army have shoulder-launched surface-to-air missiles of several states, including Stingers made in the United States," he said quoted by the Interfax news agency.

"We need to still find out who has delivered them," he said.

The United States vehemently disputed the allegation, challenging Moscow to provide proof.

"We have provided no Stingers of any kind to Syria, nor will we," said State Department spokeswoman Victoria Nuland. "If the Russian Federation has evidence of Stingers in the hands of the opposition, we'd like to see it".

Makarov said it was possible that these and other weapons could have been delivered to the rebels 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," Makarov said.

US broadcaster NBC News reported in July that the rebel Free Syrian Army had obtained two dozen surface-to-air missiles (man-portable air-defence systems known as MANPADS), delivered via Turkey.

"The Americans say that they have not delivered anything to the rebels," said Makarov.

"But we have reliable information that the Syrian rebels have foreign-made MANPADS, including American ones."

Nuland, meanwhile, noted that of all the images Washington has seen of MANPADS and MANPAD-like equipment in Syria "has been exclusively of a Soviet Warsaw Pact vintage - the SA-7 type vintage."

"We have not seen evidence of Stingers," she said.

Makarov's comments come as 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.

Turkey earlier this month forced a Syrian Air passenger plane en route from Moscow to Damascus to land in Ankara on the grounds it was carrying an illegal Russian cargo for Syria.

Turkish Prime Minister Recep Tayyip Erdogan has said the cargo confiscated by Ankara before the plane was allowed to leave was "war equipment". Russia has insisted the cargo was perfectly legal radar technology.

President Vladimir Putin last week defended Russia's right to trade weapons with whomever 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.