The Defense Ministry has doubled the number of fighter jets it scrambles when responding to airspace checks by foreign planes, government sources said Saturday.

The Air Self-Defense Force began scrambling four jets for each potential airspace violation last year, they said. The ASDF had previously been sending up only two jets per scramble since it began the practice in 1958.

As China ramps up its military activities around the Senkaku Islands in the East China Sea, scramble intercepts by both sides have been surging in areas nearby where their air defense identification zones overlap. The Japan-administered Senkakus, which lie just off Taiwan, are also claimed by China and Taiwan.