GOTEMBA, Japan (AFP) - Japan's Self Defence Forces (SDF) on Tuesday began four days of live-firing drills near Mount Fuji, in an annual exercise that comes as Tokyo tries to expand the role of the military.

About 2,300 soldiers joined the exercise with some 80 tanks and armoured vehicles as well as 60 field guns and 20 helicopters deployed at training grounds, 80km west of Tokyo.

Ground personnel fired artillery against the backdrop of Japan's highest mountain, with helicopters flying overhead.

Prime Minister Shinzo Abe is facing increasing opposition over security bills that would open the door to Japanese troops seeing combat for the first time since the end of World War II.

The controversial legislation passed through the powerful lower house of parliament last month and is being debated in the upper house.

It would allow the military to engage in combat - in defence of an ally which comes under attack - for the first time since the war.

A constitution imposed by a post-war US occupation force barred pacifist Japan's military from combat except in self-defence.

The drill coincided with a military exercise in South Korea by South Korean and US troops, which began on Monday simulating an all-out North Korean attack.

The annual Ulchi Freedom exercise, which will run through Aug 28, is largely computer-simulated, but still involves 50,000 Korean and 30,000 US soldiers.