North Korea said on Wednesday it is making progress in producing low-enriched uranium and insisted it would not accept US demands to shut down the programme.
"The construction of experimental LWR (light-water reactor) and the low-enriched uranium for the provision of raw materials are progressing apace," a foreign ministry spokesman told the official news agency.
The spokesman rejected demands by the US and its allies that the uranium enrichment plant be shut down before six-party nuclear disarmament talks can resume.
Scientists say the plant at the Yongbyon complex could easily be reconfigured to make atomic weapons. The North says it will fuel the LWR, which will be used to generate electricity.
"The right to the peaceful use of nuclear energy is an issue vital for the sovereignty and development of the DPRK (North) and, therefore, neither concession nor compromise should be allowed," the spokesman said in a statement.
Diplomatic efforts have intensified in recent months to revive the six-party talks which the North abandoned in April 2009, one month before its second atomic weapons test.
The North wants talks without preconditions and says its uranium enrichment programme -- first disclosed to the world a year ago -- can be discussed at the forum.
The US says the North must first show it is serious about the talks, which have dragged on since 2003, by shutting down the programme. The negotiations also group South Korea, China, Russia and Japan.
A website which published satellite photos said in November the North had made significant progress in building the new nuclear reactor but it was unlikely to become operational for two to three years.
Pyongyang's official news agency has previously said the reactor would start operating soon but gave no date.
The 38 North website said "significant progress" over the past year could indicate a desire to push ahead as fast as possible with uranium enrichment, to produce fuel for the reactor and possibly fissile material for weapons.
Pyongyang's existing plutonium stockpile -- estimated to be enough for six to eight atomic bombs -- came from a decades-old gas graphite reactor at Yongbyon that was shut down in 2007 under a six-party accord.
The North said on Wednesday the peaceful use of nuclear energy is the only way to solve its "acute electricity problem", a claim contested by analysts.
It said it has nothing to hide about its uranium programme and accused the United States of using it as an obstacle to a negotiated settlement of the nuclear issue.
The spokesman said attempts to make the "peaceful nuclear activities" illegal or to delay them indefinitely "will prompt resolute and decisive countermeasures".