The disappearance of a Russian-manned cargo ship in the Atlantic more than two weeks ago spawned a variety of theories and intriguing reports Thursday as the search drew in investigators from across Europe.

Russia had naval vessels and satellites scanning the ocean for the Arctic Sea — last heard from on July 28 while sailing through the English Channel with a $1.8 million cargo of timber.

Since then there has been no confirmed sighting of the Maltese-flagged freighter, which had reported being attacked July 24 in the Baltic Sea off the Swedish island of Oland.

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"There are lots of theories because no one really understands what's happening," said Pavel Felgenhauer, a security analyst. "Such wild theories circulate, because no one really understands who needs a ship with timber."

The crew had said that, on July 24, up to a dozen masked men had boarded, tied up the 15 crew members, questioned them about drug trafficking and beat them before leaving 12 hours later in a high-speed inflatable boat, the Malta Maritime Authority said.

The ship had been due to make port Aug. 4 in Algeria, but has not arrived and appeared to have changed course. The maritime authority said the Arctic Sea "has not approached the Straits of Gibraltar, which indicates that the ship headed out in the Atlantic Ocean."

Speculation on what might have happened has ranged from theories that it might have been carrying secret cargo to the possibility that it fell victim to an almost unheard of case of sea banditry in European waters.

The Swedish daily Metro said it spoke by telephone with someone who claimed to be the Arctic Sea captain on July 31 about the reported hijacking in the Baltic Sea.

"They were dressed in black uniforms," the newspaper quoted the captain as saying. "They resembled American elite soldiers and seemed very professional. They said they were looking for cocaine, which should have been loaded in Kaliningrad. They spoke English, with some kind of accent."

The ship was repaired in Kaliningrad, a Russian exclave and drug-trafficking hub, before picking up the timber cargo in a Finnish port.

Experts were wary of attributing the disappearance to bandits, noting that though piracy is rife in waters off lawless Somalia and in other areas of the world, European waters have been free of such attacks for centuries. Also, pirates usually seek ransom. They also said terrorism appeared unlikely.

"There have been rumors it can be somehow connected to the smuggling of nuclear materials, but again why should it be intercepted like that," Felgenhauer said.

More likely possibilities, he said, were insurance fraud or a commercial dispute.

"A ship can be re-registered, re-painted. It can be hijacked to change its identity, like a stolen car," he said.

Russian President Dmitry Medvedev has ordered that "all necessary measures" be taken to find the missing ship, and the Russian navy turned all of its vessels in the Atlantic — including three landing ships, a frigate and two nuclear-powered submarines — to search. The Defense Ministry said Thursday it was also using satellites.

Finnish police said they were assisting in the investigation, and France said it was in "regular contact with the authorities concerned by this affair, notably the Maltese authorities."

Britain's Foreign Office said it was monitoring developments and would provide assistance if needed.

Sweden continued to investigate the reported hijacking. The crew said the men who attacked the Arctic Sea on July 24 had identified themselves as police officers, but Swedish police said they hadn't searched any ships in that area.

Nick Blackmore, editor of the magazine Safety at Sea International, said the events that precipitated the ship's disappearance have been unusual, beginning with the alleged attack off Sweden's coast.

"It's an odd thing in and of itself because it happens so rarely in that area," Blackmore said. "We would have expected ... if they had been hijacked to call in to some port."

Blackmore said some vessels of similar specifications built in the same Turkish yard as Arctic Sea had capsized, foundered or suffered serious stability-related incidents. But he said timber floating on the sea somewhere would probably be evident if the ship had sunk.

Just after the Arctic Sea's July 28 contact, it passed through the busy Dover Strait, one of the world's busiest shipping lanes. The ship had given what appeared to be a routine report — identifying itself and its cargo, and saying where it had come from and where it was going, said Mark Clark of Britain's Maritime and Coastguard Agency.

Where the ship was next spotted is uncertain. Russian media reports say the last contact was on July 30 when the ship was in the Bay of Biscay, and that it was later spotted by a Portuguese patrol plane. Portuguese Navy spokesman Commander Joao Barbosa said, however, that the ship has never crossed Portuguese waters.

This suggests the ship may have been sailing outside of normal shipping channels.

The Finnish wood supplier that owns the cargo, Rets Timber, also had no information on the ship's whereabouts.

Experts were wary of attributing the disappearance to bandits, noting that though piracy is rife in waters off lawless Somalia and in other areas of the world, European waters have been free of such attacks for centuries. Also, pirates usually seek ransom.