Russia on Tuesday released five Japanese fishing boats detained last week near Russian-controlled islands claimed by Japan, Chief Cabinet Secretary Yoshihide Suga said, adding that all crew members are in good health.

The boats were fishing for octopus near the disputed islands when they were detained by Russian ships on Dec. 17 for investigation on suspicion they had violated fishing agreements, the Japanese government said.

"The five ships and crew members, 24 in total, left for Nemuro, Hokkaido, at around 10 a.m. (0100 GMT)," Suga told a regular news conference, referring to a port on Japan's main northern island.

"They are expected to arrive at Nemuro this evening. At the moment, there's no problem with the health of the crew members."

A Japanese news agency, quoting a Russian border guard official, said the release came after the crews paid a fine of about 6.4 million roubles ($103,000 or 11 million yen) ordered by a Russian court on Monday for violating regulations on the size of the catch Japanese vessels can take around the islands.

Following the detentions, Suga said the crews had done nothing wrong and the seizure was unacceptable.

Japan claims a string of Russian-held islands off its northern region of Hokkaido, which it calls the Northern Territories.

Known in Russia as the Southern Kuriles, the islands were invaded by the then-Soviet army in the waning days of World War II. The dispute over the islands has prevented Russia and Japan from signing a formal peace treaty.