North Korea on Tuesday warned the United States of a "horrible disaster" and put its troops on alert over a major naval drill involving a US aircraft carrier alongside South Korean and Japanese vessels.
The warning came after Seoul and Washington last week signed a new joint strategy to counter what they called 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 bellicose rhetoric to its desire to attract the United States' attention and draw it back into dialogue.
The planned naval drill in waters around the Korean peninsula involves South Korea, Japan and the United States, which has deployed the nuclear-powered carrier USS George Washington.
North Korean troops had 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 on the state news agency.
The North 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 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 drill, originally scheduled for three days from Tuesday, was postponed for a few days because of an approaching typhoon, Japan's Chief of the Maritime Staff Katsutoshi Kawano told a Tokyo press conference.
Japan will deploy two escort vessels, the Ise and the Haruyuki, for the drills which will focus on search and rescue exercises, Kawano said, adding Japan will be involved on Thursday and Friday.
He declined to comment on schedules for the US and South Korean navies.
Asked about the reaction from North Korea, Kawano said, "We will conduct search and rescue drills as scheduled, and that is all."
A spokesman for the US-South Korea Combined Forces Command had told AFP the exercise was "an annual search and rescue drill and humanitarian in nature".
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".
Professor Kim Yong-Hyun of Seoul's Dongguk University played down the North's threats, saying it was trying to draw the US back to the dialogue table.
"The North is also seeking to arouse attention in Washington with such militant statements," he said.
The United States and South Korea have long demanded that Pyongyang show commitment to ending its nuclear weapons programme before six-nation talks on the programme, which have been stalled since December 2008, can resume.
North Korea has habitually condemned joint military drills south of the border and threatened counter-attacks that have not materialised.
Professor Yang Moo-Jin of Seoul's University of North Korean Studies noted that the "emergency order" the North had issued for all its personnel was not as serious as other military alerts it issued early this year.
"The North is simply trying to draw attention from the outside world to the fact that it is closely watching the drill," he said.
"It also aims to alert its people to security threats from the United States, South Korea and Japan and pave the way for shifting blame for any military tension on the peninsula to the three."
Although the North's atomic test in February -- its most powerful to date -- sent tensions soaring, the temperature has been lowered in recent months after a series of conciliatory gestures by Pyongyang towards Seoul.
But acute concerns remain over the North's nuclear programme, with a US think tank saying last week that Pyongyang has restarted its ageing Yongbyon reactor, seen as key to boosting its nuclear weapons programme.