Japan has protested to China after a Chinese coast guard helicopter entered its airspace and four Chinese vessels entered Japanese waters near disputed islands in the East China Sea.        

Japan’s foreign ministry said its vice minister lodged a strong protest with the Chinese ambassador, urging China not to repeat such actions.   

The islands, called Senkaku in Japan and Diaoyu in China, are controlled by Japan but claimed by China, often causing tensions between the two countries.

 Japan’s defense ministry said the Chinese helicopter flew in its airspace for about 15 minutes yesterday.

In response, Japan scrambled fighter jets. Meanwhile, China claimed it used a helicopter to force a Japanese civilian plane out of the area. Chinese officials said the plane entered illegally and left five minutes later.

However, Japanese officials said China sometimes reports such incidents even when they haven’t occurred and believe the helicopter may have reacted to a Japanese civilian aircraft flying nearby.

Ongoing disputes over the islands have led Japan to strengthen ties with the Philippines and the U.S. to help counter growing Chinese assertiveness in the region.