Beijing on Sunday blasted Washington's latest intervention in the Diaoyu Islands issue, warning the US to be "responsible" and "choose its words carefully".

The warning came as Beijing prepared to receive a high-ranking member of the governing coalition in Tokyo who will reportedly deliver a letter "aimed at improving ties''.

But sending messengers to Beijing will be of little value, observers warned, if Washington's support for Tokyo's stance risks the situation getting out of control. US Secretary of State Hillary Clinton on Friday revealed Washington's lack of neutrality when she said the islands were "under the administration of Japan", a phrase that China rejects.

Clinton told reporters after meeting with visiting Japanese Foreign Minister Fumio Kishida that the US opposes "any unilateral actions" that would seek to undermine Japan's "administration", a remark observers see as clearly backing Japan.

Dong Manyuan, vice-president of the China Institute of International Studies, said Clinton's remarks show an evident preference for Japan's stance, and this runs the risk of bolstering far-right nationalists in Tokyo.

The comments are "ignorant of facts and indiscriminate of rights and wrongs", and Washington cannot deny its historical responsibility on the issue of the islands, Foreign Ministry spokesman Qin Gang told reporters on Sunday.

"Tokyo may feel less inhibited in carrying out further provocation, and the situation will become more unstable," Dong warned. "A major conflict breaking out over the islands, along with further confrontation between China and the US, does not serve US national interests."

Yet Dong added that as "Clinton is retiring soon, it remains to be seen if the incoming secretary of state, John Kerry, will follow the existing policies".

The Diaoyu Islands and affiliated islets have belonged to China for centuries, but Japan illegally grabbed the islands at the end of the 1894-95 Sino-Japanese War. Key wartime documents, including the Cairo Declaration, covered the return of the islands.

Yet, despite opposition from China, the US and Japan cut a backroom deal in 1971 giving Japan so-called "administration" over the islands.

Beijing urges the US to be "responsible" and careful with its words, Qin said.

Dong Manyuan said that perhaps Washington is also privately reining in Tokyo to prevent a serious escalation.

Meanwhile, Natsuo Yamaguchi, leader of the pacifistic New Komeito, the junior coalition partner of the ruling Liberal Democratic Party, said on Saturday night that he will take a handwritten letter from Japanese Prime Minister Shinzo Abe to Beijing.

Yamaguchi told reporters after meeting Abe that they both agreed that political talks are the "first step" to mending relations.

Yamaguchi said he hopes to deliver the letter to Party chief Xi Jinping during his four-day visit from Tuesday, Japan's Kyodo News Agency said.

The China-Japan Friendship Association, a non-governmental organization, will host Yamaguchi. It is not clear whether Yamaguchi's proposal of meeting Xi has been confirmed by Beijing.

Shotaro Yachi, a former senior diplomat now advising the Japanese prime minister on foreign policy said in an interview with Reuters that "there must be a tacit understanding between Yamaguchi and the prime minister for seeking improved ties''.

Notwithstanding Abe's proposed letter, Tokyo has not eased off on its attempts to lobby Washington for more support, said Shen Shishun, a specialist on Asia-Pacific studies at Haikou College of Economics in Hainan province.

"Tokyo's seemingly friendly postures are not feasible to resolve the tension,'' Shen warned.

Yamaguchi may press for a summit meeting between leaders of the two countries, Japanese newspaper Mainichi Shimbun said.

However, the Japanese government has long denied the existence of any dispute over the Diaoyu Islands.

The tense situation helps the Abe cabinet shift domestic public attention from the sluggish economy, said Zhu Feng, a professor of international relations at Peking University.

Shen said Japan has long been "obsessed in its illusion" of maintaining economic ties with China while posing tough on territorial disputes.

Contact the writers at zhangyunbi@chinadaily.com.cn

Pu Zhendong and Xinhua contributed to this story.