A Russian border patrol boat shot dead a Japanese crab fisherman in Russian-controlled waters near Japan's northern island of Hokkaido, highlighting continued tension between the countries over ownership of four disputed islands.

The Japanese foreign ministry protested against the shooting, saying it reserved the right to press for an apology, punishment of the perpetrators and compensation. Taro Aso, foreign minister, said he "would approach the matter with serious concern".

The ministry was also on Wednesday night pressing for the immediate release of three other Japanese crewman, all from the Nemuro peninsula on the eastern tip of Hokkaido, who were being held by Russian authorities.

Tokyo dispatched coast guard vessels to waters nearby the Russian island of Kaigara to investigate the incident.

Japan's Kyodo news agency quoted Hokkaido officials as saying that crab fishing was banned at the scene of the shooting. Officials had been told of Russian concerns about illegal Japanese fishing and had relayed the warning to local fishing co-operatives, they said.

Even if it is confirmed the Japanese crew of the boat, the No 31 Kisshin Maru, was fishing illegally, the incident will stir anger in Japan. Tokyo claims sovereignty of four nearby islands - referred to as the northern territories in Japan and the southern Kuriles in Russia - that have been administered by Moscow since the end of the war.

Return of the islands, which were occupied by Moscow while Japan was being bombed by nuclear weapons during the second world war, is a cause celebre of the Japanese right and a long-standing goal of Japan¡¯s foreign ministry. Shinzo Abe, who is almost certain to succeed Junichiro Koizumi as prime minister next month, is also a strong proponent of stepping up diplomatic efforts to press for the islands¡¯ return.

Several of the banners held up when Mr Koizumi visited the controversial Yasukuni shrine on Tuesday pressed for the return of the islands. Recently, a commercial has been aired in Japanese cinemas urging the population, the majority of which has little interest in the sparsely populated islands, to press for their return.

Failure to resolve the long-simmering dispute over the four islands has hampered diplomatic relations between Tokyo and Moscow. Commercial relations, while fast expanding in recent years, are still small compared with their potential, experts say.