The United States and South Korea have been negotiating a "strategic flexibility" plan, to turn US bases here into a regional hub for sending joint US-Korean forces under American command into potential regional conflicts.

Pyongyang, which is engaged in a tense standoff with Washington over its nuclear programme, on Tuesday again charged through its state-run media that the Western superpower was preparing to invade the Stalinist state.

The US military plan would mean a troop build-up and was "little short of a scheme to put fresh muscles into its moves for a new war of aggression in and around the peninsula," said the Minju Joson newspaper, a regime mouthpiece.

Little progress has been made on the contentious US strategic proposal, as South Korean President Roh Moo-Hyun has opposed any change in status for the 32,500 US troops stationed in South Korea.

The North has also criticised as a "war provocation" the US deployment of 15 Nighthawk stealth aircraft to the Korean peninsula this month for what US military officials on Tuesday called "routine training".

Pyongyang's state media, including the Korean Central News Agency (KCNA), on Sunday charged that the deployment of the high-tech surveillance and bomber aircraft was a prelude to a US war against North Korea.

"The US imperialist warhawks are desperately stepping up the moves to bolster up their forces... with their scenario for a nuclear war of aggression against the DPRK pushed forward at a final phase," KCNA said Sunday. "This is obviously a very (dangerous) signal predicting the outbreak of a war."

The regime's Korea Central Broadcasting Station on Monday reiterated concern about a US invasion but vowed the communist country would fight back if attacked.

"The US should bear in mind that our republic has a strong deterrence to cope with any unfair attacks," it said.

US military authorities in South Korea downplayed the deployment of the fighter jets.

"It is part of our deployment of forces in rotation," said an official for the US Forces in South Korea. "It is routine training, aimed at helping fighters familiarize themselves with the terrain."

The United States and North Korea, which US President George W. Bush has labelled as part of an "axis of evil", remain locked in a tense standoff over Pyongyang's nuclear weapons programme.

The North has boycotted China-hosted nuclear disarmament talks -- which also include the United States, South Korea, Japan and Russia -- since June last year.

In February the regime declared it had built nuclear weapons and vowed to increase its nuclear arsenals.

Pyongyang has refused to return to the talks unless Washington drops what it calls a "hostile" policy against the communist regime.