North Korea accused the United States on Monday of building up military forces in the region and vowed to strengthen its own defences "in every way".

The comments came one day after the communist state said it would bolster its nuclear deterrent in the face of what it called US antagonism.

Tensions on the peninsula have been high in recent months, following repeated threats by Pyongyang against Seoul and the North's failed long-range rocket launch in April.

South Korean and US forces will hold their largest joint live-fire military exercise Friday to showcase their "watertight defence posture and war-fighting capabilities", Seoul's defence ministry said.

The North's foreign ministry described what it termed a US arms buildup as an "open provocation" to Pyongyang and a prelude to a regional war.

The spokesman's comments on the official news agency cited the disclosure last week that US forces based in the South are seeking more attack helicopters and stronger missile defence systems.

The spokesman also mentioned a naval exercise involving South Korea, the US and Japan, to be held Thursday and Friday south of the peninsula.

South Korean and US naval forces, including a US aircraft carrier, will also hold manoeuvres in the Yellow Sea for three days starting Saturday.

The North also blasted last Thursday's Washington meeting between the US and South Korean defence and foreign ministers. It said their aim was to discuss "making South Korea an advance base for the implementation of the US strategy for domination over Asia".

The North said the US arms buildup "is a prelude to a regional war targeting not only the DPRK (North Korea) but also several Northeast Asian countries..."

Pyongyang would "increase its self-defence capabilities in every way to protect sovereignty and dignity of the country and nation".

Some Seoul analysts believe the North may engineer a border clash as new leader Kim Jong-Un tries to bolster his status with the military.

There is also speculation it will conduct another nuclear test, although Pyongyang has said it has no plans at present to do so.

The South's defence ministry said Friday's joint drill will involve some 2,000 troops, F-15K and KF-16 jet fighters, and light-attack planes.

Four US Apache attack helicopters as well as tanks and rocket launchers will fire thousands of rounds during the drill in Pocheon county, near the border.

The exercise is timed to mark the 62nd anniversary of the start of the three-year Korean War, which began with a North Korean invasion on June 25.