The families of four Russian sailors at the centre of an arms-smuggling mystery have appealed to Vladimir Putin to free them, more than 50 days after their ship was allegedly rescued from pirates.

The wives of Captain Sergei Zaretsky and three crew members on board the Arctic Sea urged the Prime Minister to intervene as a row over the cargo ship flared between its Finnish owner and Russian prosecutors. The vessel has been the focus of intense speculation that it was being used to smuggle S-300 air defence missiles to Iran after it apparently fell victim to the first act of piracy in North European waters for hundreds of years.

The women said that nobody knew where the Arctic Sea was heading after plans to dock the ship at Las Palmas, on the Canary Islands, collapsed almost three weeks ago.

“Our husbands need urgent medical and psychological help, they have been in total information isolation for 74 days,” they wrote to Mr Putin. “We ask you to assist in urgently returning our husbands home while they are still alive.”

The open letter was posted on the website of Mikhail Voytenko, a maritime expert who first reported the alleged hijacking. He has fled Russia after receiving threats from people who he said were unhappy that he had exposed the case.

Mr Voytenko posted the appeal under the headline “Is there anybody who can help the Arctic Sea or not?”

The Maltese-registered ship has been at sea since July 22, when it left Finland for Algeria carrying a cargo of timber worth $1.7 million. It was allegedly boarded by an armed gang two days later and held captive until the Russian Navy intercepted the vessel on August 17, 300 miles from Cape Verde, off West Africa, and some 2,500 miles off course.

Russia has held the ship in international waters since, despite repeated pledges to bring it into port. The ship’s owner, Solchart Management, said that it was still unable to claim the vessel three weeks after prosecutors said they had completed their investigation.

“The situation is more than strange and complicated. The cargo ship is sitting for days now 60 miles east of Gibraltar,” said Viktor Matveyev, Solchart’s chief executive. Company officials “do not understand who we should negotiate with on handing over the ship, who bears responsibility for what is happening with it”.

The Foreign Ministry in Moscow said that Russia was keen to return the ship to its owner quickly. Andrei Nesterenko, a ministry spokesman, said that it had been damaged during the hijacking and repairs required “appropriate certification” from Maltese authorities.

Eight suspects — described as two Russian citizens, an Estonian, a Latvian and four stateless persons — are in custody in Moscow accused of piracy and kidnapping. Russia insists that it found only timber on board the Arctic Sea. It fuelled speculation about a secret cargo, however, by sending three giant Il76 aircraft to Cape Verde to fly the suspects and 11 of the ship’s 15-man crew to Moscow. The aircraft are normally used to transport heavy weaponry.

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