TOKYO (AP) – Japan launched strong protest to Russia Wednesday after a Russian patrol boat opened fire on a Japanese vessel, killing a fisherman in the latest flare-up of a territorial dispute between the neighboring nations.

The crab fisherman was shot and killed near Kaigara island, off the northeast tip of Hokkaido, one of several administered by Russia and claimed by Japan.

Japan insisted the boat was in Japanese waters, called the act “unacceptable,” and demanded immediate compensation and release of the boat and surviving crew.

Russia expressed “regret” but said the shooting was justified, because the Japanese ship violated Russian waters.

They said authorities acted within their powers.

Russia’s regional border patrol said he suffered a “fatal shot in the head.”

“There has been a loss of life, and the situation is grave. Japan demands an immediate apology,” Foreign Minister Taro Aso told reporters after a tense meeting with Galuzin in Tokyo. “It’s unacceptable this took place within Japanese waters.”

The responsibility for the shootings lay “with the direct culprits and … with Japanese authorities that close their eyes to fishermen’s poaching in Russian territorial waters,” Russia’s Foreign Ministry said in a statement.

Russian officials said the man, identified by Japanese media as Mitsuhiro Morita, 35, was killed by a warning shot as he rushed to recover fishing equipment aboard the fishing boat, which was “maneuvering dangerously” and tried to ram a Russian dinghy.

“They were not aiming (to kill),” Russian Deputy Ambassador Mikhail Galuzin said.

The three surviving crew members, who were not injured, were taken to a nearby island for questioning and will face criminal charges, according to national broadcaster NHK. The three have admitted they were fishing illegally, NHK said, citing Russian investigators.

Russian officials said they had discovered freshly caught crabs on the fishing boat: Japan’s Fishery Agency acknowledged that crab fishing in that area is illegal at this time of year under an agreement between the two nations.

Morita’s mother, Shoko, said from her home in Hokkaido she couldn’t believe her son was dead.

“I don’t understand why they had to open fire,” Shoko said through tears on NHK. “He was a good son. He didn’t do anything wrong.”

The four islands – called the Kurils in Russia and the Northern Territories by Japan – were seized by the Soviet army near World War II’s end. Tokyo has demanded their return, and the dispute has blocked a treaty formally ending wartime hostilities.

The islands are surrounded by rich fishing waters and are believed to have promising offshore oil and natural gas reserves, as well as gold and silver deposits.

While Russian authorities have seized dozens of Japanese boats and injured several fishermen over the years, this was the first shooting death of a Japanese in the region since October 1956, Coast Guard officials said.

A total of 30 fishing boats and 210 Japanese crew members were seized by Russia in the disputed northern waters between 1994 and 2005. Seven fishermen were injured when the Russian coast guard fired at them during the same period, according to the Japanese Coast Guard.