MOSCOW - Russia said on Tuesday it had arrested eight people for hijacking a merchant ship off the Swedish coast and diverting it to the Atlantic Ocean — while maritime authorities pretended they had lost track of it.

Press reports said the Maltese-registered, Russian-crewed vessel had disappeared from radar screens in a maritime mystery, but the Malta Maritime Authority said on Tuesday that the Arctic Sea had "never really disappeared."

The arrests ended weeks of official silence over the ship and its $1.3 million cargo of timber, giving rise to speculation about a secret cargo and involvement in espionage.

"Eight people — citizens of Estonia, Latvia and Russia — were arrested during an operation to free the ship," Russian Defence Minister Anatoly Serdyukov told President Dmitry Medvedev in remarks posted on the Kremlin site www.kremlin.ru

"An investigation established that on July 24 these people boarded the Arctic Sea and, threatening with weapons, ordered the crew to change the route. The ship then moved on the route dictated by the hijackers towards Africa, with its navigation equipment turned off."

"This was an act of piracy," Serdyukov told reporters.

The vessel 'disappeared' in late July after heading through the English Channel towards the Atlantic. Radio contact was lost and the 4,000-tonne ship did not deliver its cargo as scheduled to the Algerian port of Bejaia on August 4.

Piracy in European waters is almost unprecedented in modern times though a wave of hijackings has plagued shipping off Somalia.

Moscow's envoy to NATO, Dmitry Rogozin, told Russian TV channels "this was a brilliant operation with disinformation used intentionally in order not to hamper the work of the military."

"NATO didn't take part in the operation but it helped locate the whereabouts of the ship," he said without elaborating.

The Malta Maritime Authority said "the movements of the Arctic Sea were always known for several days, notwithstanding reports that the ship had disappeared."

"There was consensus among the investigating authorities of Finland, Malta and Sweden not to disclose any sensitive information in order not to jeopardize the life and safety of the persons on board and the integrity of the ship," it said.

Cape Verde authorities said the Arctic Sea's crew would be taken to the island of Sal later on Tuesday before being flown to Russia. Russian television said the crew would fly to the port of Arkhangelsk in northwestern Russia, from where a replacement crew would be flown to Cape Verde.

Maritime experts have been skeptical that "traditional" pirates would target such a cargo in northern European seas, some of the world's most heavily policed.

"This was in our understanding a quite unique case, the full details of which will certainly one day be made the story of a Hollywood movie," European Commission spokesman Martin Selmayr told a regular news briefing.

EU officials said police of 22 countries had been involved in the investigation and it could be two weeks before full details emerged.

One EU official said it was not clear why it had taken several days for the ship's Finnish owners to inform the police of the incident.

"They use the term 'pirates,'" the official said of the Russian statements. "We are very careful — it's not clear whether the kind of unlawful acts conducted against this ship was piracy or another kind of unlawful act. We still need much more information."

Another official said: "We haven't seen piracy in the Baltic Sea since the 17th century and we are very cautious about calling this piracy. We have all the events off the coast of Somalia in our heads. This is totally different."