Beijing (AFP) – China on Friday scrambled fighter jets to monitor U.S. and Japanese aircraft which entered its new air defense zone, state media said.

“Several combat aircraft were scrambled to verify the identities” of U.S. and Japanese aircraft entering the air defense identification zone that Beijing declared last weekend, the state-run Xinhua news agency said, citing air force spokesman Shen Jinke.

The Chinese aircraft, which included at least two fighter jets, identified two U.S. surveillance aircraft and 10 Japanese aircraft including an F-15 warplane, Shen said.

Shen said that the air force had a mission to monitor foreign aircraft inside the zone “throughout the entire process, with timely identification”.

China’s announcement of the zone, which covers islands which are the subject of a bitter territorial dispute with Japan, has been seen as raising tensions in the region.

China’s state media called Friday for “timely countermeasures without hesitation” if Japan violates the country’s newly declared air zone.

Japan and South Korea both said Thursday they had disregarded China’s new air defense identification zone (ADIZ), showing a united front after US B-52 bombers also entered the area.