A Russian ship allegedly carrying attack helicopters and missiles destined for Syria has stopped off the Scottish coast after its British insurer withdrew cover for the vessel.

Britain said it was aware of a consignment of refurbished Russian-made helicopters on a ship heading to Syria but did not specify the vessel, and refused to confirm reports that it had alerted the insurer.

Insurer Standard Club said it had cancelled insurance for the MV Alaed, owned by Femco, a Russian cargo line, which effectively prevents the ship from sailing until the owner can secure new cover.

"We were made aware of the allegations that the Alaed was carrying munitions destined for Syria," Femco said in a statement provided to AFP.

"We have already informed the ship owner that their insurance cover ceased automatically in view of the nature of the voyage."

The BBC quoted Standard Club as saying it believed the Alaed had stopped off the coast of Scotland's Western Isles, and that it was also allegedly carrying missiles.

Several ship-tracking websites gave the same location for the ship.

The MV Alaed picked up its cargo of Mi-25 helicopter gunships from Russia's Baltic sea port of Kaliningrad, where they had been sent for servicing and repairs, Britain's Sunday Telegraph newspaper said.

Moscow originally sold them to Damascus at the end of the Soviet era.

The Daily Telegraph reported on Monday that British security services had told Standard Club that providing insurance for the shipment would breach EU sanctions.

"We are aware of a ship carrying a consignment of refurbished Russian-made attack helicopters heading to Syria," Britain's Foreign Office said in a statement.

"The Foreign Secretary made clear to Russian Foreign Minister Lavrov when they met on 14 June that all defence shipments to Syria must stop.

"We are working closely with international partners to ensure that we are doing all we can to stop the Syrian regime's ability to slaughter civilians being reinforced through assistance from other countries."

The United States notified the British government last week that the insurance on the ship was British, the Sunday Telegraph reported at the weekend.

The owner, Femco, said it had annulled a contract with the ship's current commercial operator, Denmark's United Nordic Shipping, "per mutual consent" as of Monday.

It is not clear if the decision to terminate the contract was related to the halt in the insurance policy or if there is any connection with the reported military hardware shipment to Syria.

It is also not clear how Femco could terminate an agreement which it said had never came into force in the first place and the statement offered no further details.

There was no immediate comment from United Nordic Shipping.

US Secretary of State Hillary Clinton accused Russia one week ago of fuelling the violence by sending attack helicopters to Syria, which she said were "on the way".

Russia last week said it was not making any new deliveries of attack helicopters to Syria and has only carried out repairs of helicopters sent there many years ago.

In Moscow, news reports Monday said that Russia was preparing to send two warships to the Syrian port of Tartus -- where Moscow operates a strategic naval base -- to ensure the safety of its nationals.