"Our concerned departments, including the military circles, are demanding emergency steps against the indefinite delay of the LWR [light-water reactor] construction," a commentary in the official Nodong Sinmun newspaper said.

"If the US continues to delay the LWR construction, we cannot help but do as we determined. Force must be answered with force.

"As the United States resents implementing the DPRK [Democratic Republic of Korea]-US Agreed Framework as if it were taking poison, we do not have to hold to it.

"We have suffered much loss by freezing our nuclear programme. We do not intend to suffer more," said the commentary, entitled "Have No Choice But To Take Countermeasures".

Under the 1994 Korea Peninsula Energy Development Organisation (Kedo) accord, Pyongyang agreed to scrap its nuclear weapons programme in return for $5bn in fuel and safer LWRs.

Japan, the United States and South Korea are all contributors.

Missile test

North Korea shocked the region last year when, without warning, it launched what was believed to be a medium-range Taepodong I missile over Japan and into the Pacific.

Tokyo has threatened to freeze its Kedo funding as a result of the incident, and the agreement has still to be ratified by the US Congress.

It wants assurances that North Korea is not secretly building nuclear weapons.