Finnish police said Saturday demands for an undisclosed ransom have been made for the missing freighter Arctic Sea as the search for the vessel continued, according to dpa. "I can confirm there is a question of ransom," Detective Superintendent Markku Ranta-Aho told the German Press Agency dpa. The sum was a "significant amount of money but not huge," he added, but declined to offer details of the amount or how the demand had been made to the Solchart Management shipping company, citing the ongoing criminal investigation. Finnish police were investigating suspicions of "aggravated extortion," he added. The fate of the Arctic Sea has remained a mystery since July 24 when a group of armed men allegedly posing as drugs enforcement officers boarded the vessel in Swedish waters. After 12 hours the men left the vessel without taking, anything according to the crew. The ensuing investigation has included alleged hijacking. "This is a serious crime," Ranta-Aho said, adding it was also "a matter of naval security" as the mysterious chain of events appeared to have begun in waters close to Finland and Sweden last month. Earlier Saturday, Victor Matveev, Director of Solchart Management - which owns the vessel - made no mention of any ransom demand when asked by dpa. In addition to Finnish police, authorities in Malta - where the vessel is registered - and Sweden were cooperating in the investigation and were in contact with authorities in some 20 countries via Interpol and Europol, Ranta-Aho said. Like Matveev, the Finnish police spokesman dismissed a report that the ship had Saturday shown up on the Automatic Identification System (AIS) used to identify and locate vessels. Ranta-Aho said police had no knowledge of the whereabouts of the vessel but were "eager to know if any other vessel" might have any sighting or radar contact with it. Police had good cooperation with the company, he said. The freighter left Finland on July 23, transporting lumber worth some 1.3 million euros (1.8 million dollars) en route for Algeria. Matveev said the ship had plied that route without incident for the past four years and had "very modern equipment." He expressed disappointment that a sighting reported on Friday near the Cape Verde islands proved wrong. "It is such a huge operation to find the ship, it is out of our control," he told dpa, referring to search efforts including Russian and NATO vessels. "My only concern now is the crew, I am praying for their lives." The cargo was supplied by, among others, Finnish-Swedish forestry company Stora Enso and Finnish group UPM.