The ransom demand was made to the Finnish owners of the Arctic Sea, police said, with the vessel's disappearance having set off an intense search by the Russian military and deep concern over its fate.
"Yes, it is true that there has been a demand for ransom, which is money, and the demand has been made to the company which owns the ship, Solchart Management in Finland," Finnish Detective Chief Superintendent Jan Nyholm told AFP.
The company could not be immediately reached for comment.
Officials in Cape Verde and France said on Friday the ship had been spotted off the archipelago, which lies off Africa's western coast, but Russia has not confirmed the sighting.
The French military said on Saturday it was likely the ship remained in the same area and a Russian warship seemed headed towards it.
"A small Russian frigate that was located in the Mediterranean is currently headed toward the south, probably to meet up with the Arctic Sea," said French Commander Jerome Baroe.
Moscow's ambassador to NATO, Dmitry Rogozin, said Russia would not give out details of the search for the time being.
"The data necessary to search for and identify the Arctic Sea ship is being checked and double-checked in the most thorough manner," he told Rossia television.
"The rest of the information, including the Arctic Sea's location coordinates, is not subject to disclosure," he said, citing the interests of the search operation and the crew's well-being.
A European Union spokesman has said it appeared the ship, which disappeared after passing through the English Channel in late July, had been attacked twice.
It had been due to arrive in Algeria on August 4 with a cargo of sawn Norwegian timber worth more than a million euros (1.42 million dollars).
Pirate attacks in European waters are extremely rare, and the ship's disappearance on one of the world's main shipping routes has led to intense speculation over what may have occurred.
Moscow's ambassador to Cape Verde Alexander Karpushin has said the Cape Verdean military has not officially informed him of the spotting.
He also said searches for the ship were continuing with Russian ships, submarines and satellites "and other means of detection" but declined to provide details on where they were taking place.
Experts have debated whether pirates, a mafia quarrel or a commercial dispute were behind the disappearance of the Maltese-flagged ship, which left Finland on July 23.
A European Union spokesman said Friday that the ship appeared to have been attacked twice but not in "traditional" acts of piracy.
"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, without providing details.
The ship is linked to an automatic tracking system but the last signal was received on July 30, showing it was off the coast of northwestern France.