U.S. strategic bombers joined a fleet of Japanese fighter jets in a joint military exercise meant to demonstrate their military cooperation around Japan's airspace, defense officials said Thursday, as tensions with China escalate.

Japan has scrambled jets to monitor Russian and Chinese air forces conducting joint patrols around the country, the Japanese defense ministry said late Tuesday, amid rising tensions between Tokyo and Beijing.

Japan is quickly transforming its southernmost Ryukyu islands into a heavily fortified defense zone, sparking concern and curiosity across the region. The move comes as relations between Japan and China reach levels of tension not seen in over a decade.

TOKYO (AP) — Japan and Australia urged calm on Sunday after Chinese military aircraft locked radar on Japanese fighter jets, a month after the Japanese leader’s recent remarks on Taiwan that stirred tensions between Tokyo and Beijing.

It is the first time the U.S. has criticized China for aiming radars at Japanese military aircraft as the diplomatic spat between Beijing and Tokyo shows no sign of easing.

American strategic bombers trained alongside Japanese aircraft in what Washington and Tokyo described as a demonstration of their resolve following recent military tensions between Japan and China this week.

While diplomatic tensions between the two countries are not new, both have little to gain from the current dispute subsiding.

Kareem El, a civilian from Washington, D.C., visiting Okinawa, was held by U.S. military police for declining to provide identification.