Updated 1.30 p.m.
An international criminal investigation is being held in connection with the disappearance of the Maltese-registered ship Arctic Sea, the Malta Maritime Authority said this afternoon.
It gave no information on whether or not the ship had been spotted after international reports, later denied, that it was seen of the Cape Verde islands yesterday morning.
AFP news agency said a ranson has been demanded from the Finnish owners of the ship.
"The Finnish, Swedish and Maltese authorities are conducting investigations in close cooperation into the alleged offenses relating to the cargo vessel Arctic Sea," the MMA said in a statement. The investigations involve alleged aggravated extortion and hijacking. The authority said it could not give more details at this stage.
The MMA said that authorities from more than 20 countries have contributed to the investigation, which also involves Interpol and Europol.
The European Commission expressed doubt yesterday whether the Arctic Sea, missing for more than a week, had fallen prey to pirates, as the vessel's operator had suggested.
The disappearance of the ship and its 15-member Russian crew has baffled authorities in Europe and North Africa. Moscow has sent warships to find it.
Portugal's Lusa news agency initially said the 4,000-tonne freighter was 400 miles off the West African archipelago, while France said it had intelligence of a sighting that could match the Arctic Sea.
"There was information that a cargo ship similar to the one being searched for was spotted 400 nautical miles north of the island of Santo Antao," RIA quoted Alexander Karpushin, Russia's ambassador to Cape Verde, as saying.
"However, this information did not prove to be true," he said, citing a meeting with the head of Cape Verde's armed forces.
Earlier, Lusa quoted the Cape Verde director-general of defence Pedro Reis as saying the ship was in international waters north of Sao Vicente, a Cape Verdean island close to Santo Antao.
A French naval spokesman said French intelligence had information suggesting a ship matching the description of the Arctic Sea was located north of Cape Verde. The information had been passed to Russia and Malta.
"Earlier today, French intelligence found that there was a ship in the south Atlantic, at the level (latitude) of Brazil, that could match the description of the Arctic Sea," Captain Jerome Baroe told Reuters in Paris.
Indications it was north of Cape Verde would have corroborated reports that it had been heading into the Atlantic.
However, Major Antonio Monteiro, commander of the naval squadron of Cape Verde's coast guard, said he could not confirm the information the freighter had passed north of Cape Verde.
The European Union said reported radio contacts with the ship were not consistent with usual patterns of piracy.
"Radio calls were apparently received from the ship which had supposedly been under attack twice, the first time off the Swedish coast then off the Portuguese coast," a spokesman for the executive arm of the EU told journalists.
"From information currently available it would seem that these acts, such as they have been reported, have nothing in common with traditional acts of piracy or armed robbery at sea," Martin Selmayr said.
The vessel, carrying a $1.3-million cargo of timber, was to have docked on Aug. 4 in the Algerian port of Bejaia. It never arrived and was believed to have last made contact from a position off the French coast.