Some 28 cases of North Korean boats found drifting off Japan or grounded last month raise suspicions about possible infiltration by spies
Three crewmembers from a North Korean boat have been arrested by police off Japan.
Officials say it is the latest in a growing list of incidents of North Korean boats being spotted in Japanese waters.
The three men are accused of stealing a generator from a hut on an uninhabited island off the coast near the city of Hakodate.
A boat with 10 crew was found moored at the same island last month.
Authorities say there were 28 cases of boats adrift off Japan or grounded on its shores in November, raising suspicions in the media about possible infiltration by spies from North Korea.
It is reported the bodies of dead crew have been found in a couple of cases.
Some experts, however, say the boats are just carrying fishermen, including soldiers drafted in to fish.
Authorities have ruled out that the people intercepted were attempting to defect from North Korea.