Analysts said Tokyo's political stance toward China's Diaoyu Islands will cast a shadow over relations between China and Japan, as Beijing vowed to protect its sovereignty and slammed Tokyo's plan to "nationalize" the islands.

Diaoyu Island [File photo]

"China's holy territory is not 'up for sale' to anyone," Chinese Foreign Ministry spokesman Liu Weimin said in response to remarks Japanese Prime Minister Yoshihiko Noda made on Saturday.

Noda said his government was negotiating with a "private owner" to "nationalize" part of the Diaoyu Islands.

"The Chinese government will continue to take measures needed to resolutely safeguard the sovereign rights of the Diaoyu Islands and adjacent islets," Liu said on Saturday, reiterating that China has indisputable historical and jurisprudential evidence to prove the islands and adjacent islets have been Chinese territory since ancient times.

Noda's remarks on Saturday shed light on the Japanese government's plans toward the islands. In April, Tokyo Governor Shintaro Ishihara initiated a campaign to buy the islands, eliciting protests from Beijing.

"This year marks the 40th anniversary of the normalization of bilateral diplomatic relations, and ties between China and Japan seem to be complicated on a deeper level," the Mainichi Shimbun, a leading Japanese daily newspaper, said in an article on Sunday.

Mainichi also warned that "nationalization" will lead to Chinese countermeasures.

In mid-May, Chinese Premier Wen Jiabao told Noda to "respect China's core interests and major concerns" as he reiterated China's stance on the islands.

Gao Hong, a Japanese studies researcher with the Chinese Academy of Social Sciences, said the Noda cabinet's decision on Saturday will ratchet up tensions between the two countries and set back their relations.

"This plan may affect things such as economic cooperation and bilateral public opinion, as well as geological politics," Gao said, estimating China may seek to strengthen patrols in the waters concerned to protect its sovereignty over the islands.

Many see the Noda cabinet's decision as an attempt to shift public attention from its existing political troubles and to regain public support.

The Noda cabinet is haunted by anxieties that have arisen from Ishihara's campaign to purchase the islands, the Japanese newspaper Sankei Shimbun warned on Sunday.

The Noda cabinet's decision was to some extent prompted by Ishihara, whose "purchase plan, on behalf of his prefectural government, is aimed at striking a bargain with the Japanese central government after the purchase succeeds", Zhu Jianrong, a professor of international relations at Japan's Toyo Gakuen University, told China News Service.

Meanwhile, Ishihara criticized Tokyo's decision and told reporters he will "hold his tongue and watch".

The governor also said the "private owner" of the islands is not willing to sell them directly to the country, Japan's Fuji Television reported on Sunday.

The Tokyo prefecture and the central government are "playing a two-man show", and Japan's ultimate pursuit lies in "nationalizing" the Diaoyu Islands, said Gao, adding that Tokyo's possible power reshuffle makes little difference to Japan's substantial stances on the islands issue.

Saturday is also the 75th anniversary of the July 7 Incident, which occurred on July 7, 1937, and marked the beginning of the eight-year War of Resistance against Japanese Aggression.

Li Zongyuan, deputy curator of the Museum of the War of Chinese People's Resistance Against Japanese Aggression, said "efforts to boost dialogues are indispensable" in light of the countries' tense relations over matters concerning history and territory.