Independent confirmation of the report, which was carried by several Russian news agencies, was unavailable, Reuters said.

Russia on Tuesday arrested eight people on suspicion of hijacking the Arctic Sea off the Swedish coast and sailing it to the Atlantic Ocean, ending weeks of silence about the fate of a ship, which has intrigued European maritime authorities.

The limited information from Russian authorities has failed to satisfy sceptics who voiced doubts about whether the piracy actually took place or was a convenient cover story to conceal a possible secret cargo of arms or nuclear material. Bellona’s Igor Kudrik said he believed the hijacking was a simple act of piracy that had nothing to do with nuclear materials or other illicit substances aboard the errant vessel.

"The crew members have already confirmed that the captors demanded a ransom and threatened to blow up the vessel if their orders were not obeyed," Interfax quoted a Russian Defense Ministry spokesman as saying.

"The crew members also claim that the people who seized the Arctic Sea were armed and got rid of their weapons when the ship (Russian navy ship) Ladny ordered the dry cargo carrier’s crew to stop the vessel," he said.

Climbing gear, flares and a high-speed inflatable boat supposedly used in the hijack were found aboard the Arctic Sea, RIA news agency quoted the spokesman as saying at a briefing for Russian media.

The agencies did not say what ransom was demanded, though Finnish officials confirmed to Bellona Web on Tuesday that the hijackers had contacted the Arctic Sea’s owners with a relatively low demand of $1.5 million – the approximate value of the ships cargo

Nobody answered the phone when Reuters called the ministry’s press service to attempt to verify the reports presented in Interfax and RIA Novosti – a state run news wire.