North Korea took fresh aim at the United States Wednesday over a three-nation naval drill, accusing it of "serious military provocation" and branding the exercise an "attack on our efforts for peace".

The planned drill in waters around the Korean peninsula involves South Korea, Japan and the United States, which has deployed the nuclear-powered aircraft carrier USS George Washington.

The North's foreign ministry spokesman hit out at the exercise, which comes after Seoul and Washington last week agreed a joint strategy to address what they described as the mounting threat of a North Korean nuclear attack.

The spokesman said the joint strategy signalled an increase in the "threats of nuclear war against us" and the "completion of plans for a pre-emptive nuclear strike".

"In these circumstances, the dangerous joint naval drill is a serious military provocation and a frontal attack against our efforts for peace", the spokesman was quoted as saying by the North's official Korean Central News Agency.

"We want peace but we don't beg for it. We are ready not only for dialogue but confrontation as well."

The annual naval drill had been scheduled to take place earlier this week, but was postponed due to an approaching typhoon.

It remains unclear when the drill, which the US and South Korea describe as a search and rescue exercise and humanitarian in nature, will be carried out.

North Korea on Tuesday warned the United States of a "horrible disaster" and put its troops on alert over the drill.

The United States and South Korea have long demanded that Pyongyang show commitment to ending its nuclear weapons programme before six-nation talks on disarmament, 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.

The North held its most powerful atomic test to date in February, sending tensions soaring in the region.

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 South Korea's spy agency telling lawmakers on Tuesday that Pyongyang has restarted its ageing Yongbyon plutonium reactor.