A wooden fishing boat that disappeared after washing ashore in Akita Prefecture last week with eight North Korean men aboard has been found on the seabed, Japanese authorities said Tuesday.

The sunken boat was detected by sonar equipment about 40 meters from the area where it had been moored. Local police and Japan Coast Guard personnel salvaged parts of the wreckage in the afternoon, including what appeared to be the boat's bow and stern.

The government said it will step up patrols along the Sea of Japan coast to watch for unidentified vessels and suspicious people as a number of boats, apparently from North Korea, have recently washed ashore.

"We want the police and the Japan Coast Guard to closely work together (on patrols)," Chief Cabinet Secretary Yoshihide Suga said at a news conference in Tokyo.

Suga also said he had ordered the police and the coast guard to ensure such vessels are secured and do not drift off as in the Akita Prefecture case.

The 20-meter-long vessel was found washed ashore by the police Thursday night and eight men were detained. The police were planning to check inside the boat, but a police officer noticed Saturday morning that it was no longer at the breakwater where it had been moored, possibly due to rough weather at that time.

Now that the boat has been located, the police plan to confirm whether it was from North Korea.

The men who were aboard have told Japanese authorities that they came from North Korea and were squid fishing before the boat's engine failed, according to investigative sources.