MOSCOW, August 12 (RIA Novosti) - President Dmitry Medvedev has ordered measures to track a Finnish-owned cargo ship crewed by Russians, which was last sited off Portugal's Atlantic coast on August 1 and may have been hijacked, the Kremlin said.

The order came after Solchart, the owner of the dry cargo vessel, requested Russian assistance to trace the ship on Tuesday. The relatives of the missing crew have also called on Russian authorities to help search for their loved ones.

The Arctic Sea set off from Finland on July 23, carrying timber, and was due to arrive at the Algerian port of Bejaia on August 4.

Some media reports said contact was lost with the ship on July 28, after masked men claiming to be police briefly seized the vessel in the Baltic Sea on July 24 tying the crew up and searching the vessel. A sailor was quoted by the media as saying the men left the ship after the 12-hour ordeal, and the Arctic Sea resumed its voyage.

However, suspicions are growing that the crew member could have been threatened and that the ship was in fact hijacked.

The vessel was reported to have been last seen by a Portuguese patrol boat.

Media reports said the Arctic Sea, which flies the Maltese flag, had a crew of 13 sailors on board as of late March.

Russia's Defense Ministry said later on Wednesday that it had dispatched Black Sea Fleet vessels now on a mission in the Atlantic to hunt for the cargo ship, and all search-and-rescue means, including satellite reconnaissance, have been deployed.

One of the navy vessels, the Ladny frigate, has passed the Straits of Gibraltar and is on its way to where the Arctic Sea is believed to have been last sited.

Portugal was reported to be carrying out its own search.