Eight bodies were discovered in a wooden 7-meter boat that washed ashore in Oga, Akita Prefecture, on the Sea of Japan coast facing North Korea, the Japan Coast Guard said Monday.

A cigarette pack bearing Hangul characters has been discovered from the boat, which suggests that it came from the North, Kyodo News quoted sources as saying.

The grisly discovery came just four days after eight men, believed to be North Koreans, were found drifting in a 20-meter fishing boat off the coast of Yurihonjo, also in Akita, on Thursday.

The eight survivors, who were rescued and taken into custody by Japanese authorities, have reportedly claimed they are North Koreans and were fishing in the Sea of Japan.

It was not known if the two cases were related, the coast guard said.

Parts of the eight bodies found Monday were skeletonized, indicating that a considerable amount of time had elapsed since the victims died and making it difficult to discern if they were men or women.

The coast guard has not determined the latest ship’s country of origin, a coast guard official in the city of Akita told The Japan Times by phone.

On Friday, a resident in Oga had reported to the coast guard that a dark boat had been spotted drifting about 300 meters off Miyazawa beach in Oga.

The coast guard searched the boat Sunday and Monday, discovering the eight bodies inside. It said it had found no other clues to the vessel’s origin nearby.

Separately over the weekend, the bodies of two men were found washed ashore in Sado, Niigata Prefecture, together with apparent debris from one or more wooden boats. Police suspect at least one may have come from North Korea after Korean letters were found written on its body, Kyodo News reported.

While the discoveries of wrecked wooden ships and bodies off and along the Sea of Japan coast may appear startling, a number of similar incidents have been reported in recent years.

This year alone, a total of nine bodies and three survivors have been collected from three drifting boats on and off those coastlines, excluding those found Monday and last week.

Last year, 11 bodies were found along the coastlines while 27 bodies and one survivor were found in 2015, according to the Japan Coast Guard. All are believed to have come from the Korean Peninsula, the coast guard spokesman said.

The grisly finds and rescue of survivors in the waters off the Sea of Japan coast come at a highly sensitive time for North Korea-related news, with Japanese interest high amid rising tensions with Pyongyang over its ballistic missile and nuclear weapons programs.

Meanwhile, hundreds of North Korean fishing boats have been detected in the Sea of Japan’s Yamato Bank this year. Most are believed to have been engaging in illegal poaching in Japan’s exclusive economic zone.

The coast guard has warned a total of 1,910 North Korean ships to leave that area of the EEZ, a shallow area in the middle of the Sea of Japan, since July, the coast guard spokesman said.

The Yamato Bank is a prime fishing spot, where scores of Japanese fishing boats descend in the fall to catch squid. This year, however, many have reportedly withdrawn from the area because it was too crowded with North Korean ships.

It is unclear if there are any links between those North Korean poachers and the two boats found off Akita Prefecture.