Baker said he believed the ship could reach Syria without having to stop somewhere to refuel.

An article on the website Maritime Bulletin, run by Russian maritime expert Mikhail Voytenko, said revoking the insurance would have little impact, since Russia does not support EU sanctions against weapons shipments to Syria.

The BBC reported Tuesday that the ship was about 50 miles (80 kilometers) off the Outer Hebrides off the northwest coast of Scotland. The Foreign Office and Standard Club refused to give details of its location.

U.S. Secretary of State Hillary Rodham Clinton issued a harsh reprimand of Russia last week, when she said that Moscow "dramatically" escalated the crisis in Syria by sending attack helicopters there. The State Department acknowledged later the helicopters she accused Moscow of sending were actually refurbished ones already owned by the Assad regime, but Russia was clearly annoyed, and the spat further fueled tensions between the two countries over Syria.

It was not immediately clear whether the helicopters aboard the Alaed were the ones to which Clinton had been referring.