US intelligence operatives in Turkey are vetting the flow of weapons to Syrian rebels to ensure they do not fall into the hands of Al-Qaeda militants, the New York Times reported Thursday.

The Times cited unnamed US officials and Arab intelligence officials as saying the weapons were being paid for by Turkey, Saudi Arabia and Qatar and funneled across the border by a shadowy opposition network.

The weapons include automatic rifles, rocket-propelled grenades, ammunition and some anti-tank weapons, which have allowed the rebels to fight back against the far superior forces of Syrian President Bashar al-Assad.

The Times said Central Intelligence Agency operatives in southern Turkey are overseeing the weapons shipments and gathering information on Syria's fragmented opposition.

"CIA officers are there and they are trying to make new sources and recruit people," the Times quoted an Arab intelligence official who is briefed regularly by US counterparts as saying.

The Times quoted US officials as saying they were considering stepping up aid to the rebels by providing satellite imagery and other intelligence, but had yet to take a final decision on the matter.

The Times report comes a week after US Secretary of State Hillary Clinton accused Russia of sending helicopters to its close ally Syria, sparking a row with Moscow, which has rebuffed Western calls for Assad to step down.

Washington has denied arming the opposition, and Russia has denied sending any weapons to Syria that could be used against anti-regime protesters.

Russia has also denied sending new helicopters to Syria, saying it has only carried out repairs and routine maintenance on helicopters supplied many years ago. A Russian ship allegedly carrying attack helicopters and destined for Syria was turned back from British waters earlier this week.

The Syrian revolt began in March 2011 with a wave of peaceful protests against the Assad family's 42-year reign, but has become increasingly militarized over the course of a brutal 15-month crackdown.

More than 14,400 people have been killed in Syria since the uprising began.