Japan has arrested five pro-China activists accused of landing on a Japanese-claimed island. Taiwan, China and Japan all claim sovereignty over the uninhabited outpost.
Japanese police arrested five activists who had sailed from Hong Kong for violating immigration laws.
Wednesday's maritime incident coincided with calls by China and South Korea that Tokyo face up to its wartime past as Japan marked the 67th anniversary of its World War II surrender to US-led forces in 1945.
Initially, seven pro-China protestors had tried to land on one of the chain of islands in the East China Sea known as Diaoya in China, Senkaku in Japan and Tiaoyutai in Taiwan. All three countries claim sovereignty over the unoccupied islets, situated near rich fishing waters and large maritime oil reserves.
The men, all belonging to the Action Committee for Defending the Diaoyu Islands, sought to declare China's territorial claim to a group of Japanese-controlled islands, said the protest group's leader.
The men swam to the island from their Chinese-flagged fishing vessel despite coming under water cannon fire and were apprehended shortly after making their way to shore.
"The Okinawa prefectural police arrested five men for violation of the immigration control law on Uotsuijima island," a police spokesperson told AFP.
Two of the men returned to the boat and were not arrested, but are being questioned by authorities, the group said.
"They were showing warning placards and talking through loud speakers in Mandarin to warn us off, but we just kept going," said David Ko, spokesperson for the activist group in a phone call to Hong Kong public broadcaster RTHK on Wednesday.
"The only weapon we have is to ignore them and keep going forward and that is what we are doing," he added.
Japanese officials are taking the matter up with Chinese and Hong Kong officials via diplomatic channels, Chief Cabinet Secretary Osamu Fujimura said.
Japanese Prime Minister Yoshihiko Noda told reporters he will "deal with the incident strictly in line with the law."
Shrine visit prompts protests
China and South Korea, meanwhile issued protests as two members of Noda's cabinet paid homage to 2.5 million Japanese war dead, who include 14 leading war criminals, at Tokyo's Yasukuni Shrine.
Noda, who leads Japan's fractious center-left Democratic Party cabinet, had asked his cabinet members to stay away, but one minister, Jin Matsubara, told reporters he attended in his "personal capacity."
Speaking at an official ceremony to mark the end of war 67 years ago, Noda said "enormous damage and suffering" had been inflicted by Japan last century on other countries, especially in Asia.
Beijing, referring to imperial Japan's pre-World War II occupation of parts of China, said the key issue was "whether Japan can really look in the mirror of history, heeding its lessons, holding hands with Asian people to face the future."
And, South Korean President Lee Myung-Bak urged Japan to make amends for sexual slavery forced on Korean women during Japan's former colonization of Korean territory between 1910 and 1945.
"It was a breach of women's rights committed during wartime as well as a violation of universal human rights and historic justice. We urge the Japanese government to take responsible measures in this regard," Lee said.
Japan has said it considers the issue of wartime sex slaves closed after a 1965 agreement to normalize diplomatic relations.
On Tuesday, Lee said an expression of "deepest regret" by Japanese Emporer Akihito in 1990 had not sufficed.
Last Friday, Lee visited another disputed island, known as Dokdo in Korea and Takeshima in Japan. That visit further frayed ties between the two US allies who otherwise have close economic links.
jlw, ipj/rc (dpa, AP, Reuers, AFP)