A top North Korean nuclear envoy wants to visit the United States for rare talks next month, news reports said on Saturday, amid a push by diplomats to revive negotiations on ending Pyongyang's nuclear program.

North Korea warned South Korea on Monday that any attempt to bring down the communist country would draw "strong measures" from its military, a threat issued even as Pyongyang embarked on a flurry of diplomacy with Seoul, Washington and Beijing.

Officials from the two Koreas met on Monday in North Korea to discuss their joint industrial complex just days after a gunfire exchange at sea emphasized the fragility of the peace between them.

North Korea threatened war on Sunday after South Korea warned of launching a pre-emptive strike if the North was preparing a nuclear attack - the latest salvo in a battle of rhetoric despite signs of improved cooperation across the militarized frontier.

North and South Korea opened talks Tuesday on further developing their joint industrial complex in the North despite Pyongyang's recent threat to break off all dialogue and negotiations, an official said.