North Korea has said it intends to resume building two nuclear reactors, to increase its energy capacity.
The new reactors would be much more powerful than existing facilities
The North said the move was necessary because the US had pulled out of a key deal to build it two new reactors.
But some analysts fear the North wants the reactors completed so that it can produce more plutonium with which to manufacture atomic bombs.
The North's statement will further strain its relations with the US, which have worsened since September talks.
The North had mothballed work on all its nuclear facilities, including the two graphite-moderated reactors, after it struck a deal with the US in 1994.
Yongbyon: 5 MW experimental nuclear reactor in operation, 50 MW graphite reactor under construction
Taechon: 200 MW nuclear reactor under construction
Kumho: Work on two 1,000 MW light water reactors to be built under 1994 deal abandoned
Under that agreement, it was to be built two light-water reactors (LWRs) by an international consortium. Light water reactors are much more difficult to use as a source of plutonium with which to build nuclear weapons.
But the deal broke down in 2002, when the US accused the North of admitting to a secret programme to enrich uranium for weapons' production, and last month the international consortium formally announced it was abandoning the LWR project.
North Korea has now announced plans to resume work on its 50 megawatt (MW) graphite-moderated reactor at Yongbyon, and a 200 MW graphite reactor at Taechon.
"The Bush administration's abandonment of its commitment to provide LWRs to [North Korea] compels it to develop in real earnest its independent nuclear power industry," the North Korean news agency KCNA said on Tuesday.
The agency said this was in line with its "peaceful nuclear activities".
The North has already said it has restarted work at its 5 MW reactor in Yongbyon, which is also capable of producing plutonium.
KCNA also said that the North would work on developing its own LWRs.
And it repeated an assertion made on Monday that it would "bolster its nuclear deterrent" in response to the Bush administration's "arrogant, self-justified and high-handed practices".
Earlier this month, the US ambassador to Seoul infuriated Pyongyang by labelling the North a "criminal regime" which engaged in state sponsored drugs trafficking, arms sales and currency forgery.
The North is also angered by US sanctions against North Korean companies suspected of underhand activities, including weapons sales.