TOKYO -- Japan is stepping up patrols and urging local authorities and fishermen to be on the alert after several boats thought to be from North Korea, some carrying dead bodies, were found on its northern coast.

"The coast guard and police have to cooperate to step up sea patrols around Japan," the chief government spokesman, Yoshihide Suga, said Tuesday when asked about reports that a boat carrying eight dead bodies was found on the coast of Akita prefecture, which faces North Korea across the Sea of Japan.

"The government intends to improve this to ensure we can guard against suspicious boats or people arriving in Japan," Suga said.

Get Breaking News Delivered to Your Inbox

He said local authorities, fishermen and residents should report if they spot any questionable boats or people.

Last week, police rescued eight people thought to be North Korean fishermen who ended up stranded along with their squid catch.

A week earlier, the coast guard rescued three North Korean men from a capsized fishing boat off Japan's northern coast. They were transferred hours later to another North Korean vessel that was to return them home. The coast guard later found three bodies of missing crew members from that boat, then four more bodies in another capsized boat believed to be North Korean. They were thought to have drowned.

It is unclear if the people aboard the several dozen North Korean boats that drift near Japanese shores each year are intending to defect or simply unable to make their way back aboard their unseaworthy wooden boats.

The boat recovered Monday was spotted on Saturday, but seas were too rough at the time for rescuers to approach it. It was unflagged and was reported to be "nationality unclear."

However, a coast guard official reached by phone in Akita said one of the bodies was holding a 1,000 won North Korean note, suggesting the boat was from there.

Six bodies were found inside a storage room near the bow of the boat, below deck, and another two near the stern. All were men and partially decomposed, the official said. She spoke on condition of anonymity, following coast guard policy.

The crude vessel with its very low gunwale had lost its propeller and rudder, and was similar to other poorly equipped boats often seen operating from North Korea.

Autopsies of the dead men were underway.