The warning 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 bellicose rhetoric to its desire to arouse the United States' attention and draw it back into long-stalled talks.
The naval drill in waters around the Korean peninsula, which is expected to begin Tuesday, 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 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 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."
A spokesman for the US-South Korea Combined Forces Command hinted that the military drill might have to be postponed due to an approaching typhoon.
"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.
The spokesman described the exercise as "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 Dongguk Univesity downplayed the North's threats, saying that the reclusive nation was aiming 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 the six-party talks, which have been stalled for several years, can resume.
North Korea has habitually condemned joint army drills staged south of the border and has issued threats of counter-attacks that have rarely materialised.
Professor Yang Moo-Jin of the 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 drawing 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."
The North's atomic test in February -- its most powerful to date -- triggered months of heightened military tension on the peninsula.
Tensions have eased somewhat in recent months after the North changed tack to make a series of conciliatory gestures to Seoul, including an agreement to hold family reunions for those separated during the Korean War.
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.