North Korea has warned the United States of a "horrible disaster" and put its troops on alert over a joint naval drill involving a nuclear-powered US aircraft carrier alongside South Korean and Japanese vessels.

The warning on Tuesday came after Seoul and Washington last week signed a new joint strategy to counter the growing threat of a North Korean nuclear attack after the communist country restarted an ageing plutonium reactor.

That accord also drew a sharp rebuke, with analysts attributing the isolated regime's recent aggressive rhetoric to its desire to arouse the US' attention and draw it back into long-stalled talks.

The naval drill in waters around the Korean peninsula had been scheduled to begin on Tuesday, but could be postponed or cancelled due to Typhoon Danas making its way towards the area.

North Korea has habitually condemned naval drills there and has issued threats of counter-attacks that have rarely materialised.

'Imperialist aggression'

The North Korean troops have been ordered to "keep themselves fully ready to promptly launch operations any time", a spokesman for the General Staff of the Korean People's Army said, in a statement carried by the state-run Korean Central News Agency.

North Korea said the situation on the peninsula was "getting strained again" and warned the US that the closer its forces came "the more unpredictable disasters their actions will cause".

The US should bear in mind that the Korean people and army are highly alert to promptly and confidently cope with and foil blatant provocations of any hostile forces in the world with its own powerful military muscle. Spokesman for the General Staff of the Korean People's Army

"The US will be wholly accountable for the unexpected horrible disaster to be met by its imperialist aggression forces," the statement said.

"The US should bear in mind that the Korean people and army are highly alert to promptly and confidently cope with and foil blatant provocations of any hostile forces in the world with its own powerful military muscle."

"The joint exercises will be conducted this week as planned. But like any other maritime exercises, we will continue to monitor weather conditions and adjust them as necessary", he told AFP news agency.

The spokesman described the exercise as "an annual search and rescue drill and humanitarian in nature".

Reacting to the threats, South Korean Defence Ministry spokesman Kim Min-seok said the South's armed forces were "closely monitoring North Korean military's movements and fully prepared to take a decisive action against the North's possible provocations."

A US defence official speaking last week in Tokyo called the three-nation drills "increasingly common" and "designed to strengthen coordination and improve readiness to respond to situations such as humanitarian assistance and disaster relief".

The US and South Korea have long demanded that Pyongyang show commitment to ending its nuclear weapons programme before the six-party talks, which have been stalled for several years, can resume.

The impoverished North's large but ageing conventional military is considered unfit to fight an extended modern battle, but it staged surprise attacks against the South in 2010 that killed 50 people in aggression unprecedented since the war.

In March, the North declared it was no longer bound by the armistice that ended fighting in the 1950-53 Korean War signed with the United States and China, threatening to use nuclear weapons to attack US and South Korean territories.

It is believed to have enough fissile material to build up to 10 nuclear bombs, but most intelligence analysis says it has yet to master the technology to deploy such weapons.