The leaders of China and Japan met Wednesday for only the second time since taking office, but the effort to repair badly damaged ties was marred after Prime Minister Shinzo Abe earlier failed to apologise for Tokyo's wartime aggression.

Chinese President Xi Jinping and Japan's Abe met on the sidelines of a summit in the Indonesian capital Jakarta for about 30 minutes, seeking to fix a relationship damaged by territorial disputes and a bitter wartime legacy.

Shaking hands before the talks started, the two men looked more relaxed than at their meeting at a summit last November in China, where they shared an awkward handshake.

Following the talks Abe, whose strident nationalism has caused much friction with Beijing, told reporters the leaders had a "very meaningful summit meeting" and relations between China and Japan were improving.

But a speech by Abe at the summit earlier Wednesday, in which failed to apologise for Japan's World War II rampage through Asia, cast a shadow over the talks, with Xi afterwards referring to "historical issues".

"I hope the Japanese side can take seriously the concerns of its Asian neighbours," CCTV News reported Xi as saying.

A commentary on Beijing's official Xinhua news agency said the meeting was a positive sign but added Abe's failure to apologise was "deeply regrettable" and Tokyo's "treacherous stance on the sensitive historical issues" was holding back the relationship.

Beijing and Tokyo's historically frosty relations have plunged to their lowest level in decades over competing claims to Japanese-controlled islets in the East China Sea and China's view that Abe is not sufficiently repentant for Japan's 20th century wartime aggression.

In Abe's speech to the gathering of Asian and African leaders, he expressed "deep remorse" but did not make a "heartfelt apology" or refer to "colonial rule and aggression", failing to echo the language of a landmark 1995 statement on Japanese wartime behaviour.

At an Africa-Asia summit in Jakarta in 2005, then-Japanese leader Junichiro Koizumi used the phrasing that Abe omitted.

For China and South Korea, which suffered under the yoke of Japan's imperial ambition, Abe's language is a crucial marker of Tokyo's acceptance of guilt for its march across Asia in the 1930s and 1940s which left millions dead.

- Bad omen -

In addition to Xi's comments following the talks, South Korea's foreign ministry expressed "deep regret" at Abe's omission of the key phrases.

His remarks at the start of the two-day summit were potentially a bad omen for a statement he is due to make later this year marking the 70th anniversary of the end of World War II.

Observers are waiting to see whether he will make direct reference to his country's "colonial rule and aggression" and express remorse and apologise, as previous premiers did on the 50th and 60th anniversaries.

Abe suggested in a TV interview this week that he will not repeat a formal apology in the statement.

As well as the statement later this year, attention will also focus on Abe's choice of words about the war when he heads to the United States this weekend on a week-long trip, during which he will address a joint session of Congress.

In the Jakarta speech Abe also made a veiled attack on China over ongoing maritime disputes. "We should never allow to go unchecked the use of force by the mightier to twist the weaker around," he said.

In addition to its maritime dispute with Japan, China has arguments with several other countries over its claims to much of the South China Sea.

Abe's Jakarta speech was just his latest move that risks inflaming regional tensions -- it came after he sent an offering this week to the controversial Yasukuni Shrine in Tokyo, the supposed repository of the souls of the country's war dead including 14 war criminals.

On Wednesday more than 100 Japanese lawmakers visited the shrine, which China and South Korea view as a symbol of Japan's unwillingness to repent for its aggression.