WASHINGTON: US officials accused North Korea of flouting UN sanctions and seeking to destabilize the region amid the latest claims that the secretive state has built a sophisticated, new uranium enrichment plant.

“This validates a long-standing concern that we’ve had with respect to North Korea and its enrichment of uranium,” said the US top military officer, Admiral Michael Mullen, adding that Pyongyang has consistently denied any enriching.

The news also highlights that North Korea “is led by a dictator… who constantly desires to destabilize the region,” the chairman of the Joint Chiefs of Staff told ABC television Sunday.

He was reacting after an American scientist revealed he had toured a modern, new uranium enrichment plant equipped with at least 1,000 centrifuges on November 12 at the Yongbyon nuclear complex.

Stanford University professor Siegfried Hecker called the facility “stunning,” adding he was told it was already producing low-grade uranium although there was no way to confirm if the plant was fully operational.

“It is possible that Pyongyang’s latest moves are directed primarily at eventually generating much-needed electricity,” he wrote in his report. “Yet, the military potential of uranium enrichment technology is serious.”

Hecker, who is reported to have briefed the White House, said he had been astonished by his findings.

“Instead of seeing a few small cascades of centrifuges, which I believed to exist in North Korea, we saw a modern, clean centrifuge plant of more than a thousand centrifuges all neatly aligned and plumbed below us,” he wrote.

His guides told him there were in fact 2,000 centrifuges which were already producing low-grade enriched uranium to help fuel a nuclear power reactor, and insisted it was for a civilian nuclear electricity program.

In Seoul, the top US envoy on North Korea said the latest news was “very unfortunate” but “not a crisis.”

“We’ve known about this for some time,” Stephen Bosworth told South Korean Foreign Minister Kim Sung-Hwan in Seoul, Yonhap news agency reported.

“It’s a very unfortunate development, but it’s not a crisis.”

The US envoy said the program violated a United Nations resolution and a September 2005 six-nation agreement, under which the North agreed to scrap its nuclear programmes in return for aid, diplomatic and security benefits.

However, Bosworth, who will go on to Japan and China, said he does “not at all rule out the possibility of further engagement with North Korea”.

US Defense Secretary Robert Gates, traveling in Bolivia, told reporters that he believed Pyongyang has had an ongoing nuclear power program “for a long time” and that “an enrichment plant like this, assuming that is what it is, obviously gives them the potential to create a number more.”

“North Korea has ignored a number of Security Council resolutions. They continually try to export weapons. So the notion they have developed this, is obviously a concern,” Gates said.

Gates said that if the reactor is for civilian nuclear power “then they should welcome the IAEA,” the UN nuclear agency.

North Korea, which has carried out two nuclear tests, withdrew from the denuclearization talks — involving the two Koreas, China, Japan, Russia and the United States — in 2009.

The regime also announced last year it was restarting its Yongbyon complex, outside the capital Pyongyang, after UN condemnation and sanctions.

Mullen said Pyongyang had routinely denied enriching uranium, and said North Korean leader Kim Jong-Il must have flouted UN sanctions to be able to build the facility.

A senior official in Obama administration described North Korea’s claim of a new plant as “a provocative act of defiance.”

Hecker said North Korean scientists told him that construction work on the facility, dubbed the “Uranium Enrichment Workshop,” started in April 2009 — the same month that Pyongyang withdrew from the six-party talks — and was completed just a few days ago.

US Senate Foreign Relations Committee chairman John Kerry said the report was “troubling” and urged both the United Nations and China to step up enforcement of the sanctions.

Hecker, who used to direct the Los Alamos National Laboratory, had already revealed when he left North Korea that North Korean leaders claimed to be building an experimental light-water nuclear reactor to be completed by 2012.

A leading US research institute said last week the new reactor could be used to make weapons-grade plutonium.

In recent months North Korea has expressed some willingness to return to stalled six-party talks. And some administration officials speculated Pyongyang might have decided to show off its new facilities hoping to win US concessions if the talks resume.