North Korea said Wednesday it is making rapid progress in enriching uranium and building a new reactor -- projects which experts say could give it a second way to make nuclear weapons.

"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 United States and its allies that the uranium enrichment plant be shut down before long-stalled six-party nuclear disarmament talks can resume.

The North says the uranium plant at its Yongbyon atomic complex will fuel the LWR, which in turn 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.

The announcement appeared to put a damper on diplomatic efforts to revive the six-party talks, which the North abandoned in April 2009. One month later it staged its second atomic weapons test.

The North wants talks to resume without preconditions and says its uranium enrichment programme -- first disclosed to visiting US experts one 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.

US Secretary of State Hillary Clinton, speaking at an aid forum in the southern South Korean city of Busan, called on the North "to take concrete steps that promote peace and stability and denuclearisation".

The North's strong statement is "seen as a message to Washington at a time when Clinton is in South Korea", Dongguk University professor Kim Yong-Hyun told AFP.

Pyongyang was not saying it would boycott six-party negotiations but "strongly urging the US and its allies to make concessions", he said.

Siegfried Hecker, one of the US experts who visited Yongbyon in November 2010, said both the experimental light-water reactor and the uranium enrichment plant appeared designed mainly for civilian nuclear power.

But he said the plant could readily be converted to produce highly enriched uranium for bombs and the LWR could be run to produce plutonium.

A website that published satellite photos said in November the North had made significant progress in building the new reactor but it was unlikely to become operational for two to three years.

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 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 nuclear settlement.

The spokesman said attempts to make the "peaceful nuclear activities" illegal or to delay them indefinitely "will prompt resolute and decisive countermeasures".