TOKYO (Reuters) - Japanese police arrested three crew of a North Korean boat on Saturday for stealing a generator from a hut on an uninhabited island, public broadcaster NHK said, the latest drama amid increasing arrivals of North Korean fishing boats off Japan.

The boats, some in distress, some abandoned and some with dead bodies on board, have raised fears about infiltration by spies as tension with North Korea surges over its missile and nuclear programs. North Korea has test-fired two missiles over Japan, a country it has threatened to destroy.

Most experts say the wooden boats are just carrying fishermen including soldiers drafted to fish. There has been no suggestion the crew are defectors.

A boat, with 10 crew on board, was found moored at the island, off Hokkaido, last month and several crew said they picked up electronic goods from the hut, according to NHK.

Police arrested three of them for theft and other crew members will be sent to the Immigration Bureau, NHK said.

Hokkaido police were not immediately available to comment. A spokesman at the Japan coast guard declined to comment.

There were 28 cases of boats adrift off Japan or grounded on its shores in November, the coast guard has said, compared with just four in November last year.