Two Japanese cabinet ministers visited a shrine honouring war criminals Wednesday on the anniversary of Tokyo's 1945 surrender, a move set to inflame feelings already running high over territorial spats.

The visits come as Japan is embroiled in a worsening dispute with South Korea over islands that lie half way between the two nations and as pro-Beijing activists attempt to land on another archipelago at the centre of a row.

Jin Matsubara, who handles the issue of Japanese kidnapped by North Korea, and land minister Yuichiro Hata went separately to Yasukuni Shrine, which honours 2.5 million war dead -- including 14 leading war criminals from World War II.

Visits to the shrine by government ministers spark outrage in China and on the Korean peninsula, where many feel Japan has failed to atone for its brutal expansionist adventurism in the first half of the 20th century.

In a speech underlining the historical hangover, South Korean President Lee Myung-Bak called on Japan to face up to responsibility for the women who were forced into sex slavery for Japanese soldiers during the war.

"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," he said.

Around 500 South Koreans, including two former comfort women, rallied outside the Japanese embassy to stage their 1,035th weekly protest over the issue, which Tokyo insists was settled in a 1965 accord normalising relations.

Wednesday's protest came a day after Lee said Japan's Emperor Akihito would have to apologise for past excesses should he wish to visit South Korea.

Tokyo rounded on Lee, who had previously been viewed as a pragmatist with whom it could deal.

Foreign Minister Koichiro Gemba said his comments on the emperor -- a respected figurehead in Japan -- were "extremely regrettable".

"It is difficult to comprehend why President Lee made remarks like that yesterday," Gemba told reporters, adding Tokyo had lodged a protest through diplomatic channels.

The pilgrimages to Yasukuni were the first on the sensitive anniversary by any government minister since the centre-left Democratic Party of Japan came to power in 2009.

All three prime ministers since then have asked their cabinets to stay away.

At the shrine, Matsubara told reporters he was there "in a personal capacity" and had used his visit to "remember ancestors who established the foundations of the prosperity of present-day Japan".

Those enshrined at Yasukuni include General Hideki Tojo, the Japanese prime minister who ordered the attack on Pearl Harbor and was convicted of war crimes and hanged by a US-led tribunal.

Seoul had on Tuesday urged the ministers not to go to the shrine on the date it marks as Liberation Day, commemorating the end of Japan's often harsh colonial rule of the Korean peninsula from 1910 to 1945.

Lee caught Tokyo off guard last week when he travelled to Seoul-controlled islands in the Sea of Japan (East Sea), known as Dokdo in Korean and Takeshima in Japan.

Tokyo recalled its ambassador in protest and made noises about cancelling planned summits.

Separately, Japan is embroiled in a rumbling dispute with Beijing over islands in an area of the East China Sea believed to be rich in mineral deposits.

A group of pro-China activists from Hong Kong and Macau were reportedly near the disputed islands -- known as Senkaku in Japanese and Diaoyu in Chinese, where they claimed Japan's coastguard had fired water cannon at them.

Their voyage is aimed at pressing the Chinese claim to the uninhabited but strategically coveted archipelago.

Some 6,000 Japanese, led by Emperor Akihito and Empress Michiko as well as Prime Minister Yoshihiko Noda, offered silent prayers at noon for the war victims at a memorial ceremony in Tokyo.

Their speeches used tried and tested forumlae for regret, but avoided an explicit apology.

"During the war, (Japan) inflicted significant damage and pain on many countries, especially on people in Asian countries," Noda told the annual ceremony. "We deeply regret that."

Akihito said: "Recalling history, I profoundly hope that the suffering of war will never be repeated. I sincerely express mourning for those who lost their lives on the battlefields, and wish world peace and our country's further development."