North Korea on Tuesday lashed out at an upcoming joint US-South Korean military exercise, warning it would attack the South and the US mainland in case of any armed provocation.

The South and its close US ally will next month hold their largest-ever annual exercise in response to the North's recent nuclear test and long-range rocket launch, Seoul's defence ministry has announced.

The North's military supreme command said the allies planned to practise a "beheading operation" aimed at the North's leadership, and other moves to neutralise its nuclear weapons and missiles.

If there were even a "slight sign" of special forces moving to carry out such operations, the military said, "strategic and tactical" preemptive attacks would be launched.

The primary target would be the South's presidential Blue House, it said in a statement on the official news agency, condemning it as "the centre for hatching plots for confrontation with the fellow countrymen in the north, and reactionary ruling machines".

The North also threatened attacks on US bases in the Asia-Pacific and the mainland.

It said it has "the most powerful and ultra-modern strike means" in the world capable of "dealing fatal blows at the US mainland any moment and in any place".

Such blows would "reduce the cesspool of all evils to ashes, never to rise again on our planet", it added in a reference to the United States.

The North habitually claims that the annual Key Resolve/Foal Eagle exercise is a rehearsal for invasion while Seoul and Washington say it is purely defensive.

Tensions are high as the United Nations considers tougher sanctions against the North to punish it for January's nuclear test and this month's rocket launch.

The South, in an unprecedentedly tough move, has shut down a Seoul-financed and jointly-run industrial estate in the North, saying it was helping finance its neighbour's military programmes.