'Big secret'

There has been much confusion over the fate of the Arctic Sea after the ship's owner reported that the crew had claimed the vessel had boarded by masked men on July 24 near the Swedish island of Gotland.

The pirates reportedly tied up the crew, beat them, claimed they were looking for drugs, then sped off about 12 hours later in an inflatable craft.

But by the time that report emerged from the Swedish police, the ship had already passed through the English Channel, where it made its last known radio contact on July 28.

Speaking to Al Jazeera, John Burnett, a maritime security consultant, said: " [It's] an extraordinary mystery, it's probably an unsolved mystery until the Russian government decides to let us in on the big secret.

"This is no piracy, and no common hijacking, it's nothing like we've seen in Somalia, you don't hijack a ship that is carrying $1.3m of timber, and a ship that isn't worth very much.

"If it was captured, I would use the word captured not hijacked, by some forces then it was done so for a reason, far beyond normal hijacking or piracy.

"The talk in the London maritime community is that it was carrying something dangerous or something very nasty.

"It could have been anything from a CBRN (chemical, biological, radiological and nuclear) device, or pieces of something like that.

"It came from Kaliningrad, it could have had one object or several objects, and then been loaded with timber."

'Alive and well'

The Arctic Sea had been due to arrive in the Algerian port of Bejaia on August 4.

But when a week passed without the vessel turning up Medevedev ordered the defence ministry to use all means necessary to find it.

Shortly after the ship had been recovered on Monday, Serdyukov had told Medvedev that the crew were "alive and well".

"The crew have been transferred to our anti-submarine ship, the Ladny, where they are being questioned to clarify all the circumstances of the disappearance," he said.

Authorities in Praia, the capital of cape Verde, said the Ladny was heading for the island of Sal where a Russian aircraft was standing by to fly the group home.

Finnish investigators reported on Saturday that the ship's owners had received a ransom demand, but it was not clear if the demand came from people linked to those onboard the vessel or was a hoax.