By Kento Sahara and Nobuhiro Kubo

TOKYO (Reuters) - South Korea expressed deep regret and China's state-run news agency called on Tokyo to repent its wartime past on Monday after dozens of Japanese lawmakers visited a shrine for war dead, which Seoul and Beijing see as a symbol of Tokyo's wartime militarism, on the anniversary of Japan's World War Two defeat.

Japanese Prime Minister Shinzo Abe sent a ritual offering but did not go to the Yasukuni Shrine. Visits to the shrine outrage Beijing and Seoul because it honours 14 Japanese leaders convicted by an Allied tribunal as war criminals, along with war dead.

Ties between China and Japan, Asia's two largest economies, have been strained in recent days after a growing number of government ships sailed near disputed East China Sea islets.

Territory disputes and historical issues also periodically chill relations between Japan and South Korea.

"(We) express deep concern and regret that responsible political leaders ... are again paying tribute to the Yasukuni Shrine that glorifies the history of the war of aggression," South Korea's Ministry of Foreign Affairs said in a statement.

China's Xinhua news agency urged Japan to repent its wartime past or risk steering the country down a dangerous path.

"It's in the interests of both Japan and its neighbouring countries for the former military power to truly reflect upon its past wrongs," Xinhua said in a commentary.

Abe has not visited the shrine in person since December 2013, sending ritual offerings instead.

"He told me to come and my visit was out of respect to those who gave their lives for the country," said Yasutoshi Nishimura, an aide in Abe's Liberal Democratic Party (LDP), who gave the offering in Abe's name as LDP president rather than premier.

New Defence Minister Tomomi Inada, who has been accused by China of recklessly misrepresenting history after she declined to say whether Japanese troops massacred civilians in China during World War Two, was visiting troops in Djibouti and unable able to go to the shrine as she has in the past.

Emperor Akihito, at a ceremony honouring victims of the war, expressed "deep remorse" over the conflict fought in the name of his father, Hirohito. He first used the phrase at the memorial service last year - the 70th anniversary of the war's end - in what some saw it as a subtle rebuke to Abe, who favours a less apologetic tone.

"Reflecting on our past with a feeling of deep remorse, I earnestly hope the ravages of war will never be repeated," said Akihito, 82. The emperor hinted in a rare video address last week at wanting to abdicate in a few years.

Abe vowed at the same ceremony that Japan would work for world peace.

"Going forward, and sticking to this firm pledge while facing history with humility, we will make every effort to contribute to world peace and prosperity and the realization of a world where everyone can live without fear," he said.

(Additional reporting by Kiyoshi Takenaka and Takaya Yamaguchi in Tokyo and Nataly Pak in SEOUL; Writing by Elaine Lies and Linda Sieg,; Editing by Paul Tait and Nick Macfie)