Japan has reportedly set a direction for strengthening its combined exercises with the United States, mobilizing nuclear-capable bombers to counter growing threats from North Korea's ballistic missiles.

Japan's Kyodo News agency issued the report on Sunday, quoting a Japanese government official.

In December last year, Japan approved three security-related strategic documents, including the revised National Security Strategy, in which it decided to strengthen fast deterrence options. The reported move appeared to be aimed at demonstrating U.S. nuclear deterrence as part of the options.

The United States and Japan staged joint air exercises with South Korea involving the U.S. B-1B strategic bombers on February 19, a day after North Korea fired what it claims is a Hwasong-15 intercontinental ballistic missile, which landed in Japan's exclusive economic zone.

A Japanese official reportedly said that the United States is quickly responding to the North's provocation since last year at the request of South Korea and Japan.