Japan's incoming Prime Minister Shinzo Abe will send a special envoy to China, media reports said, amid tension over the Diaoyu Islands.

Beijing blasted controversial provisions on Sunday in a defense bill passed by the US Senate, which acknowledges "the administration of Japan" over the islands and urges arms sales to Taiwan.

Observers said that Abe's gesture does not mean any concessions on the islands are in the offing.

The bill passed in the US Senate, they added, will fuel regional instability and damage trust-building efforts between China and the US.

Abe, leader of Japan's Liberal Democratic Party will become prime minister on Dec 26.

He is considering sending LDP Vice-President Masahiko Komura, head of the Japan-China Friendship Parliamentarians' Union, to China.

"Abe's envoy plan is simply posturing, rather than an act of sincerity,'' said Lu Yaodong, from the Institute of Japanese Studies at the Chinese Academy of Social Sciences.

Ties were soured in September after the Japanese government illegally "purchased" part of the Diaoyu Islands.

Abe declared on Saturday that he would postpone his campaign proposal of sending government personnel to the islands, Japan's Kyodo News Agency said.

The Japanese Air Self-Defense Force sent fighter jets on Saturday to an area some 100 kilometers north of the Diaoyu Islands after a plane of China's State Oceanic Administration was spotted patrolling, according to the Japanese Defense Ministry.

On Friday, Chinese marine surveillance vessels patrolling the waters around the islands found six Japanese coast guard ships illegally entering the area, and demanded they leave at once.

Lu said Tokyo's hard line "has been and will be consistent".

Feng Wei, a specialist on Japanese studies at Fudan University in Shanghai, estimated that Abe's incoming Cabinet will not make a major concession due to support both within the country and from the US.

The US Senate passed the 2013 Defense Authorization Act on Friday by 81 votes to 14. It now awaits the signature of US President Barack Obama.

Though the US takes no position on the ultimate sovereignty of the Diaoyu Islands, section 1286 said "it is the sense of Congress that'' it "acknowledges the administration of Japan'' over them.

And section 1281 said, "it is the sense of Congress that ... the president should take steps to address Taiwan's shortfall in fighter aircraft, whether through the sale of F-16 C/D aircraft or other aircraft of similar capability''.

Foreign Ministry spokeswoman Hua Chunying said on Sunday that China is "deeply concerned and firmly opposed" to the contents concerning China in the act.

Hua said the Treaty of Mutual Cooperation and Security between the US and Japan is a "bilateral arrangement in a specific historical time'', and such a pact should not harm the interests of any third parties including China.

Dong Manyuan, vice-president of the China Institute of International Studies, said the bill shows bipartisan consensus on the islands as well as Obama's increased determination to focus more on Asia in his second term.

Tao Wenzhao, a professor of US studies at the Chinese Academy of Social Sciences warned that the bill sends "erroneous signals to right-wing radical Japanese politicians who are yearning for more support from Washington to rein in China, and are undermining the strategic trust between Beijing and Washington".

As for the act's arms sales proposal, Hua, the ministry spokeswoman, said China is firmly opposed to arms sales to Taiwan by any country.

Dong said the arms sales issue is not an isolated case and outside forces may be attempting to undermine rapidly developing cross-Straits ties.

Orville Schell, director of Center on US-China Relations at Asia Society in New York, said: "My reading of the Obama administration is that they don't want this (tension between China and the US) to escalate out of control.''

The US is deeply dedicated to working out a better relationship with China, Schell added.

Chen Weihua in New York and Xinhua contributed to this story.

Contact the writer at zhangyunbi@chinadaily.com.cn