Japan and the United States have started talks on operational plans in the case of armed conflict over a group of East China Sea islets claimed by Tokyo and Beijing, Japanese media said on Thursday, prompting China to complain of "outside pressure".
The dispute in recent months had escalated to the point where both sides scrambled fighter jets while patrol ships shadow each other, raising fears that an unintended collision or other incident could lead to a broader clash.
The United States, which has announced a security "pivot" towards Asia, has said repeatedly it takes no position on the sovereignty dispute, but believes it is important for China and Japan to work out their differences peacefully.
Shigeru Iwasaki, head of the Japanese Self-Defence Forces' joint staff, and Samuel Locklear, commander of U.S. forces in the Asia-Pacific, are expected to agree that the allies will accelerate the drafting of the plans when they meet in Hawaii on Thursday and Friday, Kyodo news agency said.
They will likely review several scenarios including one under which Japanese and U.S. armed forces conduct joint operations in case China invades the islands, Kyodo said. The Nikkei business daily carried a similar report on Wednesday.
"China is extremely concerned by these reports ... The Chinese government has the determination and ability to maintain the nation's territorial sovereignty," Chinese Foreign Ministry spokesman Hong Lei said.
"No outside pressure will affect the resolve and determination of the Chinese government and people to maintain territorial sovereignty."
The rocky, uninhabited islets, called the Senkaku in Japan and Diaoyu in China, are located near rich fishing grounds and potentially huge oil and gas reserves.
Senior U.S. officials including State Secretary John Kerry have said in recent months that the islands are covered by the Japan-U.S. Security Treaty.
Asked about the media reports, Japanese Chief Cabinet Secretary Yoshihide Suga said Tokyo and Washington had been in close cooperation on security matters, but declined to comment on what will likely be discussed at the meeting.
China is also in dispute with several Southeast Asian countries over parts of the South China Sea also potentially rich in natural resources.