US and Japanese fighter jets have carried out joint air exercises, according to an official, just days after Chinese and Japanese military jets shadowed each other near disputed islands in the East China Sea.
The five-day exercise involved six US FA-18 fighters and around 90 American personnel, along with four Japanese F-4 jets and an unspecified number of people, the official said on Tuesday.
The drill was carried out over Pacific waters off the coast of Shikoku, the fourth largest of Japan's islands.
It came just weeks after Shinzo Abe became Japan's prime minister after winning an election on campaign promises to reinvigorate his country's security alliance with the US and take a more robust line against China.
The exercise also coincided with a dispute between China and Japan over the sovereignty of the disputed East China Sea islands shows no signs of letting up.
Japan reportedly scrambled fighter jets on Thursday to head off Chinese military jets in an area adjoining the airspace of the Japanese-controlled Senkaku islands, which China claims as the Diaoyus.
A Chinese defence ministry official later said two J-10 fighters flew to the area to monitor two Japanese F-15 fighters that had trailed a Chinese Y-8 aircraft, according to China's official Xinhua news agency.
On Tuesday, one Chinese state-owned Y-12 plane flew close to, but not inside, the airspace of the disputed islands, triggering the scrambling of Japanese fighter jets, the defence ministry in Tokyo said.
The row between Asia's two largest economies over the uninhabited, but potentially resource-rich islands blistered in September when Japan nationalised three of them.
Chinese government ships have repeatedly gone to the archipelago's territorial waters since then.
China insists it is simply patrolling islands it has owned since ancient times.
Commentators say China wants to prove that Japan does not have effective control over the chain and draw Japan into concessions.
On Sunday, Japan's Ground Self-Defence Force carried out the nation's first military exercise designed to recapture "a remote island invaded by an enemy force".
About 300 troops took part in the 40-minute drill with 20 warplanes and more than 30 military vehicles at the Narashino Garrison in Chiba, southeast of Tokyo.
Another 80 personnel from the SDF's First Airborne Brigade rappelled from helicopters to demonstrate manoeuvres to counter an enemy invasion of a remote island.
In October Japan and the US dropped plans for a joint drill to simulate the retaking of a remote island, reportedly because Japan did not wish to provoke China further.
There was no outward indication that the joint Japan-US exercise that began Monday and runs until Friday was aimed at China, and the area being used was a long way from any contentious zone.
While the security alliance receives wide public support in Japan, there are tensions between bases and their host communities, particularly over noise and the risk of accidents, as well as associated crime.