“We don’t know what she is carrying. We only know there’s timber, but whether there is something else will be established by investigators,” Makarov said on Wednesday, adding that the “motive for the hijacking is not clear”.

Earlier, Bastrykin said he “didn’t exclude” the possibility, that the ship had undeclared cargo, and that was one of the reasons why the released crew members, who have been transported to Moscow for interviewing, had been “held for a time”. “We need to make it clear that they have no connection with the events,” he said.

More shadow was cast on the already-murky hijacking story on Tuesday, when the Russian Foreign Ministry announced that the Arctic Sea captain had tried to play off the vessel as a North Korean ship. The motives for this move are not yet clear.

The Arctic Sea, carrying a load of timber from Finland, was due to arrive in Algeria on August 5. On July 24, she was boarded by eight people traveling on a speedboat, who allegedly threatened the crew with arms, and forced them to change the course and disable communication equipment.

After several weeks of conflicting media reports and official statements, the vessel was re-captured by the Russian navy near the Cape Verde Islands on August 17. Of the people arrested for the alleged seizure, several turned out to have criminal records. They deny any wrongdoing and claim to be members of a private environmental group, whom the vessel crew rescued after an incident. All eight are now being held in custody in Moscow. They have been charged with kidnapping and piracy.

The Arctic Sea is now manned by four original crew members and is proceeding from the Cape Verde Islands to the Black Sea port of Novorossiysk. She is expected to arrive in early September, after which a throughout search of the vessel is due to be conducted.