Experts said Washington believes that backing Tokyo will have long-term benefits.

Lyu Yaodong, an expert on Japanese diplomacy at the Chinese Academy of Social Sciences, said Obama is "determined to see tangible progress in his rebalancing strategy" during his Asian trip, and "to achieve this goal, satisfying demands from Japan regarding the islands is necessary".

Students use hugs to ease Sino-Japanese tensions

Special: China-Japan relations

Abe told reporters on Thursday that "the Japan-US alliance is more robust than ever before."

"The US pivot cannot succeed without strong support from important allies such as Japan," Lyu said.

Ruan noted a shift in the US-Japan military relationship, and one example is that the US is "outsourcing" more defense duties to Japan.

"Washington believes that its promise on the islands is a feasible way to strengthen its influence over Japan, and accordingly Washington wants Japan's self-defense forces to play a greater role, which is very dangerous," Ruan said.

Yang, the Defense Ministry spokesman, also confirmed what Chinese Navy Commander Wu Shengli said on Wednesday about a worst-case scenario.

Wu told reporters on the sidelines of the Western Pacific Naval Symposium that the possibility of a military conflict remains between China and Japan, and the priority is to "prevent the outbreak of a conflict".

Yang also said the PLA will continue military patrols in waters near a tropical Japanese island close to Taiwan, days after Tokyo announced it would break ground on a new radar base in the area.

The radar station on Yonaguni Island, just 150 km from the Diaoyu Islands, marks Japan's first military expansion at the western end of its island chain in more than 40 years.

"We are paying close attention to Japan's military trends," he said.

"China's military will continue to carry out battle readiness patrols, military drills and other activities in the area," Yang said.