Chinese Premier Wen Jiabao heralded warmer ties with Japan on Thursday, calling for a "win-win relationship" between the countries' economies even as he urged politicians to face up to Tokyo's wartime aggression.

But Wen's conciliatory note was dampened by an ongoing spat over undersea gas and oil deposits, with China's Foreign Ministry asserting exploration rights in disputed waters between the two neighbors.

Wen was on a three-day "ice-melting" trip to Japan as the two countries worked to reverse a deterioration in ties caused partly by disagreements between the former World War II enemies over their painful past.

In a speech to Japan's parliament — the first by a Chinese leader in 22 years — Wen said he did not want to "dwell on hard feelings" but urged politicians "to remember and learn from the past. He also told Japanese parliamentarians hoped Japan's apologies would be "turned into actions."

The two countries have long been at odds over Japan's invasions and occupation of China in the 1930s and '40s. China has accused Japan of not fully atoning for its aggression, while some Japanese feel their leaders have apologized enough and that accounts of Tokyo's wrongdoings have been exaggerated.

Still, much of Wen's remarks focused on cooperation between Asia's largest economies. China, including Hong Kong, is Japan's No. 1 trading partner, and Beijing is eager to boost Japanese technological assistance and investment in its booming economy.

"The Chinese and Japanese economies have a win-win relationship. Our economic development poses the other no threats, only opportunities," he said in a speech met with standing ovation from the floor.

Wen later had lunch with the heads of some of Japan's largest businesses, including Toyota Motor Corp. CEO Fujio Cho, where he recited a poem that ended "the winter has passed, and spring has come" in China-Japan relations.

At the lunch, he urged Japanese companies to invest in China, vowing to address vast imbalances in the Chinese economy, improve the natural environment, protect intellectual property rights, continue tax breaks for high-tech companies and remain committed to currency reform.

He then met Japanese Prime Minister Shinzo Abe to launch annual discussions between the countries' finance and economic ministers to further boost ties. The first meeting will take place in Beijing later this year.

Wu's visit comes amid an improvement in ties that began when Abe traveled to China in October on a fence-mending visit, after bilateral relations plunged during the 2001-06 term of his predecessor, Junichiro Koizumi.

Chinese leaders were especially irked by Koizumi's repeated pilgrimages to a Tokyo war shrine that honors Japan's war dead, including executed war criminals. Abe has so far stayed away from the shrine, though he was a regular visitor before he took office.

In a sign of warming relations, Wen's visit has involved a series of friendly gestures aimed at the Japanese public.

He promised to send two Chinese ibises to a Japanese bird reserve when he met Abe on Wednesday, and appeared for a jog at a Tokyo park early Thursday, even joining a group doing tai chi. On Friday, he was to throw pitches with college baseball players in western Japan.

Wen also met with Japanese Emperor Akihito on Thursdsay and invited him to the opening ceremony of the 2008 Beijing Olympics. Akihito, who last visited China in 1992, said he would consult with his government advisers, according to palace officials.

But even as Wen struck a friendly note, a dispute over undersea gas and oil deposits threatened to sour the fragile detente.

Tokyo expressed concern on Thursday over a report by China's state-controlled CNOOC Ltd. that said it began producing oil and gas from a disputed field between the two countries. Japanese officials have asked China for more details of the CNOOC report, a Foreign Ministry official said on customary condition of anonymity.

Japan has objected to China's exploitation of the gas, saying some belongs to Japan. China insists that the field lies in its territory.

"It is a natural exercise of our legitimate sovereign rights and interests," Chinese Foreign Ministry spokesman Qin Gang said Thursday at a regular briefing. "We hope Japan will have a clear understanding of this point."