The plans are expected to be included in a revised national security strategy and mid- to long-term defence guidelines later this year. A move to develop strike capability is a major shift for Japan's self-defence-only principle, though the country has rapidly expanded its military's role and capability in the past decade to work more closely with the United States and other partners in the region and Europe.

Japan and the United States began a major joint military exercise on Thursday in southern Japan as the allies aim to step up readiness in the face of China's increasing assertiveness and North Korea's intensifying missile launches.

The biennial "Keen Sword" drills kicked off at a Japanese air base in southern Japan and will also be held in several other locations in and around Japan through November 19.

About 26,000 Japanese and 10,000 American troops, as well as 30 vessels and 370 aircraft from both sides, are to participate in the drills, according to the Japanese Defence Ministry.

Australia, Britain and Canada will also join parts of the drills, it said.

Joint field trainings that include amphibious landing exercises are planned on southwestern Japanese remote islands, including Tokunoshima, Amami and Tsutarajima, as Japan has been bolstering its defence capability in the region amid growing tensions over China.

China has reinforced its claims to virtually the entire South China Sea by constructing artificial islands equipped with military installations and airfields. Beijing also claims a string of islands that are controlled by Japan in the East China Sea, and has stepped up military harassment of self-ruled Taiwan, which it says is part of China to be annexed by force if necessary.

The joint exercise also comes on the heels of intensifying missile firings by North Korea, which has launched more than 30 of them this year, including one on Wednesday that fell in the sea between the Korean Peninsula and Japan.

Last month, an intercontinental ballistic missile flew over northern Japan.

Prime Minister Fumio Kishida, citing worsening security in the region, has pledged to substantially increase Japanese military capability and possibly allow pre-emptive strike capability to attack enemy missile launch sites from afar.

The plans are expected to be included in a revised national security strategy and mid- to long-term defence guidelines later this year.

A move to develop strike capability is a major shift for Japan's self-defence-only principle, though the country has rapidly expanded its military's role and capability in the past decade to work more closely with the United States and other partners in the region and Europe.

Exercises like Keen Sword provide Japanese and US forces "opportunities to train together across a variety of mission areas in realistic scenarios to enhance readiness, interoperability, and build credible deterrence," US Forces Japan said in a statement on Thursday.