MOSCOW: Russia said Tuesday it had arrested eight men for hijacking the Arctic Sea ship whose disappearance in July sparked an international sea hunt.

The two Russians, four Estonians and two Latvians were detained at sea after the Russian navy took control of the ship at an undisclosed location believed to be off the west coast of Africa.

"These people, claiming their boat had engine problems, boarded the Arctic Sea and, using the threat of arms, demanded that the crew follow all of their orders unconditionally," Defence Minister Anatoly Serdyukov said.

The Arctic Sea saga started after the cargo ship left a port in Finland on July 23 and disappeared from radars shortly after, sparking a massive naval hunt.

But even with the arrests important questions remain over what happened to the vessel. A respected Russian shipping expert, Mikhail Voitenko, said he believed important aspects of the story were being covered up.

Serdyukov said the Arctic Sea was hijacked in Swedish territorial waters in the Baltic Sea and added that the operation to rescue the crew was accomplished without a shot being fired.

"Eight people -- not members of the crew -- have been detained," he added, in remarks to President Dmitry Medvedev reported by Russian news agencies.

The crew of the Maltese-flagged, Russian-owned ship set a course for Africa and turned off all navigational and tracking equipment under orders from the pirates, Serdyukov said.

An investigation was underway aboard the Russian warship Ladny, where the 15 crew members and suspected pirates were being questioned, the reports quoted Serdyukov as saying.

He said the operation to "liberate" the 3,988-tonne ship came after coordinated action between Russian naval and air force units, but did not elaborate.

Arrangements were being made to repatriate the Russian crew, he added.

Officials in Praia, the capital of the Cape Verde archipelago, said that a Russian transport plane was on standby on the island of Sal waiting for the Ladny to put into port with the crew and fly them back to Russia.

Serdyukov first announced Monday that the Arctic Sea had been found 300 kilometres (485 miles) off Cape Verde and its crew taken aboard the Ladny, an anti-submarine warfare vessel involved in the search.

There was still no word on the exact current whereabouts of the Arctic Sea itself.

Medvedev on Monday called for a full investigation of the Arctic Sea mystery and vowed that "all interested parties" would be informed on the results.

The official story is that the Arctic Sea was sailing from Finland to Algeria with a crew of 15 and a cargo of sawn timber estimated to be worth 1.16 million euros (1.64 million dollars).

Speaking at a Moscow news conference, Voitenko, editor of the online Sovfrakht Maritime Bulletin and an experienced seaman, listed five reasons why the official version was suspicious.

These included the delay in initial reports the ship had been attacked and the lack of distress signals despite sophisticated communications equipment aboard the vessel and crew mobile phones that would have been in signal range.

"I believe the countries involved found a solution and agreed to 'keep it in the family' without having the time to find a plausible explanation" for the mysterious voyage, Voitenko said.

Finnish authorities on Sunday dismissed talk that the Arctic Sea was carrying nuclear material.

Jukka Laaksonen, head of the Finnish Radiation and Nuclear Safety Authority, said firefighters conducted radiation tests on the ship at a port in Finland before it began its voyage.