North Korea says it is making rapid progress on work to enrich uranium and build a light-water nuclear power plant, increasing worries that the country is developing another way to make atomic weapons.

Pyongyang's foreign ministry said in a statement that the construction of an experimental light-water reactor and low enriched uranium were "progressing apace".

It added that North Korea had a sovereign right to the peaceful use of nuclear energy and that "neither concession nor compromise should be allowed".

Concerns about North Korea's atomic capability took on renewed urgency in November 2010 when the country disclosed a uranium enrichment facility that could give it a second route to manufacture nuclear weapons, in addition to its existing plutonium-based programme.

North Korea has been building a light-water reactor at its main Yongbyon nuclear complex since last year. Such a reactor is ostensibly for civilian energy purposes, but it would give the North a reason to enrich uranium. At low levels, uranium can be used in power reactors, but at higher levels it can be used in nuclear bombs.

Earlier this month, North Korean state media said "the day is near at hand" when the reactor will come into operation. Washington has concerns about reported progress on the reactor construction, saying it would violate UN security council resolutions.

The US secretary of state, Hillary Clinton, speaking to reporters on Wednesday at an international aid forum in the South Korean port city of Busan, did not address the North's statement on uranium. She called the US-South Korean alliance strong and mentioned the recent first anniversary of North Korea's artillery attack on a frontline South Korean island that killed four.

"Let me reaffirm that the United States stands with our ally, and we look to North Korea to take concrete steps that promote peace and stability and denuclearisation," Clinton said.

Five countries, including the US, have been in on-again, off-again talks with North Korea to provide Pyongyang with aid in exchange for disarmament. North Korea pulled out of nuclear disarmament talks in early 2009 in protest at international condemnation of its prohibited long-range rocket test.

In recent months North Korea has repeatedly expressed its willingness to rejoin the talks, and tensions between the Koreas have eased. Diplomats from the Koreas and the UShave had separate nuclear talks, and cultural and religious visits by South Koreans to the North have resumed.

South Korean and US officials, however, have demanded that Pyongyang halt its uranium-enrichment programme, freeze nuclear and missile tests and allow international inspectors back into the country before resuming negotiations.

The North Korean statement on Wednesday accused the U S and its allies of "groundlessly" taking issue with the North's peaceful nuclear activities. They are "deliberately laying a stumbling block in the way of settling the nuclear issue on the Korean peninsula through dialogue and negotiations", the statement said.

Kim Yong-hyun, a professor at Dongguk University in Seoul, said the North's statement appeared aimed at applying pressure on Washington and the international community to rejoin the nuclear disarmament talks quickly. "North Korea is expected to step up its rhetoric," he said.