China remains irreconcilable over its stance on the Diaoyu Islands sovereignty issue, Vice Premier Li Keqiang Tuesday told a visiting delegation of US diplomacy and national security heavyweights, which reportedly came to mediate worsening Sino-Japanese ties.

Li met with White House Assistant for National Security Affairs Stephen Hadley, former Deputy Secretary of State James Steinberg and former Assistant Secretary of Defense Joseph Nye, according to Xinhua.

After talking about Sino-US relations, Li expressed China's "solemn stance" on the Diaoyu Islands issue, stressing that the international community should join hands in preserving the fruits of World War II and the post-war world order, Xinhua reported.

China has insisted on its sovereignty over the Diaoyu Islands, and holds that Japan has stolen the islands from China.

Chinese foreign ministry spokesman Hong Lei said on Monday that the delegation would focus on Sino-US relations.

"Hong's remarks indicated that China will not accept the mediation of the US, which has not shown any sincerity in defusing the Diaoyu Islands dispute so far," Wang Pin, a researcher on Japanese studies with the Chinese Academy of Social Sciences, told the Global Times Tuesday.

While the US is scurrying to prevent military clashes between the two Asian giants so that its own interest would not be harmed, it is also trying its best to encourage Japan to boost its defense to contain China, Wang said.

While visiting Japan on Monday, US delegation member Richard L. Armitage, the former deputy secretary of state, suggested Japan reinforce its defensive capabilities to deter Chinese provocations over the islands in a review in early October, Japan Times reported.

Meanwhile, both Japan's Ministry of Foreign Affairs and the office of Deputy Prime Minister Katsuya Okada have denied that Okada had acknowledged the existence of the dispute over the sovereignty of the Diaoyu Islands, in comments made on Hong Kong-based Phoenix Television Monday.

In the latest flare-up, Japan spotted a Chinese scientific research ship and four marine surveillance ships in waters about 20 kilometers northwest of the Diaoyu Islands, ribenxinwen.com quoted the Japan Coast Guard as saying.