China welcomed Japanese Prime Minister Shinzo Abe on Sunday with a 21-gun salute, meetings with its top three leaders and glowing state media headlines about the first official visit of a Japanese head of state in five years. But the threat of a North Korean nuclear test clouded the trip that has been heralded as a turning point in China-Japan relations.

North Korea declared last week that it would conduct its first nuclear test to bolster defenses against the United States. Sunday was considered a likely date because it is the anniversary of Kim Jong Il's taking leadership of the Korean Workers' party.

The possibility that North Korea will still carry out its threat can't be ruled out, Abe said. "In my meeting with President Hu Jintao, we saw eye to eye that the North Korean announcement of its intent to conduct a nuclear test can never be tolerated" because it threatens the peace and security of East Asia and the international community.

Both China and Japan will step up coordination, Abe added, to "induce North Korea to return unconditionally" to the six-party talks aimed at its nuclear disarmament, talks that Pyongyang has boycotted for a year.

Other than expressing "deep concern," China's Foreign Ministry had less to say about North Korea. The window to six-party talks was still open, said spokesman Liu Jianchao, and "the best way to solve this problem is through dialogue and consultation."

But a professor at the influential Central Party School argued that China's approach to its reclusive neighbor had been too soft.

"South Korea, Russia and China share the same idea on this -- no war, no sanction, no violence against North Korea. These countries have given Kim Jong Il a wrong signal, a protective screen, that he can do whatever he wants," said Zhang Liankui, a North Korea expert and professor at the school's Institute for International Strategic Studies. "Peaceful negotiation had been undertaken many times, but what is the result? It is a failure."

Chinese scholars and officials who believe a nuclear test is simply a way to force concessions from the United States are wrong, Zhang argued. The tactic simply buys North Korea more time to develop its nuclear weapons, which threaten China and other Asian neighbors more than they threaten the United States, he said.

Abe is to fly to South Korea on Monday for talks expected to focus on North Korea.

Highlighting the importance of his state visit to China, Abe was greeted with fanfare. On Sunday, toward the end of a national holiday and on the first day of a major Communist Party congress, China arranged rare access to its top three leaders and an assurance that China was confident Japan would not glorify its past military aggression nor gloss over its war criminal history.

In return, hard-liner Abe vowed to look squarely at a history that had "left scars" in other Asian countries.

Until this weekend, China-Japan relations have been at their lowest level in years. China canceled previous meetings with Abe's predecessor, Prime Minister Junichiro Koizumi, after he made repeated visits to the controversial Yasukuni Shrine, which honors Japan's war dead, including 14 convicted war criminals.

Abe has not explicitly said he will not visit the shrine.

But strong economic relations are now forcing the mending of political ties. Japan's trade with China has doubled over the past five years, surpassing Japan's trade with the United States. It is an investment that has helped create 10 million jobs in China, Abe said.

"In the past, Japan has brought enormous harm and catastrophe on Asian people. Japan has expressed deep remorse for this and this will not change," spokesman Liu described Abe as saying. "Japan will never glorify its militaristic past and will never gloss over class-A war criminals in the Second World War."

At a news conference, Abe echoed the tough language about Japan's past. "We shall look at past history squarely and shall continue to conduct [ourselves] as a peaceful nation. Japan has come through the 60 years of the postwar period on the basis of a deep remorse that Japan in the past had caused tremendous damage and suffering to the people of countries, especially Asian countries, and left scars in those people," Abe said. "This feeling is shared by people who have lived these 60 years and a feeling that I also share. And this feeling will not change in the future."

Liu described a 90-minute meeting between Abe and Chinese President Hu, which was followed by an 80-minute meeting with Chinese Premier Wen Jiabao and a 40-minute meeting with Wu Bangguo, head of China's parliament. It was a lot of attention for the suddenly planned visit.

Abe chose China over the United States for his first overseas trip, less than two weeks after becoming prime minister. He arrived to complimentary state media headlines announcing the landmark two-day visit: "The wise take advantage of opportunity."

Researcher Jin Ling contributed to this report.