Russia may decide to fly a controversial military cargo of helicopters and air defence systems to Syria after it abandoned an attempt to ship the materiel by sea, a report said Wednesday.

The West wants Russia to halt all military cooperation with Syria because of the escalating conflict between the Damascus regime and rebels but Moscow has insisted it cannot break contracts.

A freighter, the Alaed, at the weekend docked in the Russian Arctic port of Murmansk after turning back off the British coast from a voyage to Syria to deliver the military cargo when its British insurer dropped cover.

"The three Mi-25 helicopters and air defence systems could easily be delivered to Syria by air," a military source, who was not identified, told the Interfax news agency.

"Russia has to fulfill its obligations. But everything will depend on if we can resist pressure from the West who want us to break military cooperation with Syria," the source said, adding a decision would be made soon.

Russian Foreign Minister Sergei Lavrov has confirmed the Alaed was carrying three attack helicopters Moscow had repaired for Damascus under a previous agreement.

He said last week the cargo also included air defence systems but gave no further details on the type or quantity on board.

Russia delivers a range of limited air defence systems to Syria but reportedly has refused to provide the more advanced S-300 technology that it had previously also failed to give to Iran under Western pressure.

The Vedomosti business daily reported on Tuesday that Russia this year chose to withhold the S-300 from Syria, despite a $105 million delivery contract being signed by the system's producer and Damascus in 2011.

Military experts have speculated that the Alaed was carrying the more basic Russian Buk-M2e air defence systems for Syria, whose forces last week shot down a Turkish warplane off the Syrian coast.

In Murmansk, the Alaed's flag has been changed to a Russian flag from that of the Caribbean island of Curacao.

But Russia has yet to confirm if the ship will now make a repeat attempt to reach the Syrian port of Tartus or travel on to Russia's Far East port city of Vladivostok as originally planned.