China said it would lodge a complaint with Japan after it detained Chinese activists who landed on a disputed island and raised a flag on Wednesday, as tension between Japan and its neighbors escalated on the anniversary of the end of World War Two.

The landing by the activists on an island chain in the East China Sea and their detention by Japan's coastguard came on a day of regional diplomatic jousting, underscoring how history haunts Japan's ties with China and South Korea.

Earlier, South Korea prompted an official protest from Japan after comments by South Korean President Lee Myung-bak which some saw as going too far by insulting Japanese Emperor Akihito.

And in a move likely to add to the anger of Japan's neighbors, two Japanese cabinet ministers paid homage at a controversial Tokyo shrine for the war dead.

Memories of Japan's wartime occupation of much of China and colonization of South Korea run deep despite close economic ties in one of the world's wealthiest regions.

Japan arrested five members of a group of activists from China, Hong Kong and Macau who landed on the island, Japan's coastguard said. China's Xinhua news agency said Japan's coastguard later arrested nine activists on their boat.

Japanese media also said that in all, 14 activists had been detained.

Japan protested to China's ambassador over the landing and Prime Minister Yoshihiko Noda said Tokyo would deal with the matter strictly in accordance with the law.

In response, China's Foreign Ministry said it was "contacting the Japanese side to lodge representations over five Chinese nationals' detention on the Diaoyu Islands", referring to the isles known as Senkaku in Japan. It did not mention the nine detained on their boat.

China's Xinhua state news agency said Japan had pushed tension "to a new high".

"The tensions are fully due to irresponsible clamoring and attempts by some Japanese politicians and activists to claim the islands, which ... indisputably belong to China," it said.

Friction over the uninhabited isles, near potentially rich gas deposits, had already been heating up.

Several of the activists, who set out from Hong Kong, jumped into the sea, swam and waded ashore. The group said its boat had been rammed by the coastguard and hit with water cannon. A Japanese official denied that any serious damage had been done to the boat.

Media published photographs of the activists planting a Chinese flag on a rocky shore.

"We've waited 10 years for this ... We finally managed to get ashore," the captain of the protest ship was quoted as saying on Hong Kong television.

Xinhua said earlier the activists might be sent back to Hong Kong, which could help to keep the feud from escalating.

A separate row over rival claims by South Korea and Japan to other rocky islands has also intensified, signaling how the region has failed to resolve differences nearly seven decades after Japan's defeat at the end of World War Two.

The friction in part reflect skepticism over the sincerity of Japan's apologies for wartime and colonial excesses.

On Tuesday, South Korea's Lee told a group of teachers that Emperor Akihito should apologize sincerely if he wants to visit South Korea, saying a repeat of his 1990 expression of "deepest regrets" would not suffice.

TANGLED HISTORY

Japan, noting that it had never broached the idea of a visit by the emperor to South Korea, lodged a protest with Seoul over the remarks. Akihito has spent much of the past two decades trying to heal the wounds of a war waged in his father's name.

Lee, whose Friday visit to the island claimed by South Korea and Japan frayed ties between the two U.S. allies, called Japan an "important partner that we should work with to open the future".

But in remarks commemorating Korea's liberation from Japan's 1910-1945 rule, he also said the countries' tangled history was "hampering the common march toward a better tomorrow".

He urged Japan to do more to resolve a dispute over compensation for Korean women abducted to serve as sex slaves for wartime Japanese soldiers, known by the euphemism "comfort women" in Japan and long a source of friction.

"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 says the matter was closed under a 1965 treaty establishing diplomatic ties. In 1993, Tokyo issued a statement in the name of its then-chief cabinet secretary apologizing to the women and two years later set up a fund to make payments to the women, but South Korea say those moves were not official and so not enough.

Speaking at a ceremony marking the war's end on Wednesday, Japanese Prime Minister Yoshihiko Noda acknowledged the "enormous damage and suffering" caused by Japan to other countries, especially in Asia.

"We deeply reflect upon (that) and express our deepest condolences to the victims and their families," he said, vowing that Japan would never go to war again.

Tapping into anti-Japanese sentiment remains a way to seek public support in South Korea and China, which face leadership changes in coming months. And some experts see a new strain of nationalism is surfacing in Japan amid gloom about the future.

In a sign of the domestic pressures in Japan, National Public Safety Commission Chairman Jin Matsubara and Transport Minister Yuichiro Hata visited the Yasukuni shrine for war dead, defying Noda's urgings to stay away.

Many see the shrine as a symbol of Japan's past militarism because 14 Japanese wartime leaders convicted as war criminals by an Allied tribunal are honored there with Japan's war dead.