N. Korea says uranium program nearly complete

SEOUL, South Korea -- North Korea said Friday it is on the threshold of mastering a new way of building atomic bombs, pressuring the United States to agree to direct negotiations or see the communist regime become a greater nuclear risk.

Pyongyang's claim to have succeeded in experimental uranium enrichment -- an easier way to make nuclear weapons -- raises concerns that North Korea may add uranium-based weapons to enlarge its stockpile of atomic bombs made from plutonium.

North Korea also said it is continuing to weaponize plutonium.

The tough talk came as Washington showed no signs of easing pressure on North Korea despite its recent series of conciliatory gestures, including releasing two detained American journalists and reportedly inviting top U.S. envoys to Pyongyang.

"We are prepared for both dialogue and sanctions," the North said in a letter to the U.N. Security Council carried Friday by its official Korean Central News Agency. If some veto-wielding permanent members of the council put "sanctions first before dialogue, we would respond with bolstering our nuclear deterrence first before we meet them in a dialogue," it said.

The Security Council slapped tough sanctions on North Korea for conducting an underground nuclear test in May.

The North said it does not oppose the denuclearization of the Korean peninsula, but warned it would be left with no choice but to take "yet another strong self-defensive countermeasure" if the standoff continues. It did not elaborate on possible countermeasures.

The letter stressed "the denuclearization of the Korean peninsula is closely related with the U.S. nuclear policy towards the DPRK." Those are the initials for the Democratic People's Republic of Korea, the country's official name.

The letter was sent to U.S. Ambassador Susan Rice, this month's president of the Security Council. The U.S. mission said it was received Thursday and sent to the 14 other council members that night.

U.S. State Department spokesman Ian Kelly said the North's announcement was troubling.

"We are very concerned by these claims that they are moving closer to the weaponization of nuclear materials, but I can't really comment on the veracity, how true these claims are," Kelly said.

Security Council diplomats said they do not anticipate a council meeting on the letter or a new U.N. resolution.

The United States and other members have been focusing on implementation of the council resolution adopted unanimously in June after the North violated a previous resolution by conducting a suspected ballistic missile test and a second nuclear test. The resolution imposed tough new sanctions on the reclusive communist nation's weapons exports and financial dealings, and allows inspections of suspect cargo in ports and on the high seas.

The U.S. has pressed for North Korea to return to six-party talks on its nuclear program. The North pulled out of the negotiations with the U.S., South Korea, China, Russia and Japan after the council criticized its April rocket launch.

Pyongyang said later it won't return to the negotiations and will only talk one-on-one with the Obama administration.

Analysts said the North appears to be trying to add urgency to the standoff to get Washington into one-on-one talks.

"I think this is a 'let's-have-direct talks' message," said Yang Moo-jin, a professor at Seoul's University of North Korean Studies. "The North is saying that the more delayed U.S.-North Korea talks are, the greater its nuclear capabilities will become."

Washington's special envoy on North Korea, Stephen Bosworth, is in the region for discussions with China, South Korea and Japan over how to bring Pyongyang back to six-nation talks that the North has boycotted since earlier this year.

South Korean media reported last week the North invited Bosworth and chief U.S. nuclear negotiator Sung Kim to visit Pyongyang for their first nuclear talks since President Barack Obama took office. Washington has said it has no plan to send them.

Bosworth said Friday any nuclear development in North Korea was a matter of concern.

"We confirm the necessity to maintain a coordinated position and the need for a complete denuclearization of the Korean peninsula," he said in Beijing. He also said the U.S. is willing to have direct talks with Pyongyang, but only within the framework of the six-nation disarmament talks.

The letter from North Korea's U.N. Ambassador Sin Son Ho, obtained by the Associated Press, accused the Security Council of operating a double-standard and said it should apologize rather than impose sanctions.

If the Security Council had not made an issue of North Korea's "peaceful satellite launch in the same way as it kept silent over the satellite launch conducted by South Korea on Aug. 25, 2009, it would not have compelled the DPRK to take strong counteraction such as its second nuclear test," the letter said.

North Korea said it was "fair and square" that it took "self-defensive steps" against the threats aimed at depriving the country "of its rights to peaceful economic construction."

North Korea has long sought direct negotiations with Washington. It says it needs nuclear weapons to protect itself against a threat from the U.S., which has 28,500 troops based in South Korea. North and South Korea technically remain at war because their three-year Korean War ended in 1953 with a truce, not a peace treaty.

The U.S. had long suspected the North also had a covert uranium enrichment program, which would give it a second source of nuclear material. North Korea for years denied the claim but revealed in June it was prepared to start enriching uranium.

Verifying the North's claim on uranium enrichment won't be easy, South Korean Defense Ministry spokesman Won Tae-jae said, adding it could be a negotiating tactic.

Uranium can be enriched in relatively inconspicuous, underground factories, and could provide North Korea with an easier way to build nuclear bombs, experts say. Uranium-based bombs may also work without requiring test explosions like the two carried out by North Korea this May and in 2006 for plutonium-based weapons.

The North's announcement suggests the regime has made progress in research and development in its uranium program in a small pilot factory, said Lee Choon-geun of South Korea's state-funded Science and Technology Policy Institute. Still, he said it could take at least five years to build a uranium-based bomb.

The U.S., China, Japan, Russia and South Korea have tried for years to persuade North Korea to dismantle its plutonium-based nuclear program -- which experts say has yielded enough weaponized plutonium for at least half a dozen bombs -- in exchange for much-needed aid.

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Associated Press writers Kwang-tae Kim, Wanjin Park in Seoul, Edith M. Lederer at the United Nations, Chi-Chi Zhang in Beijing, Shino Yuasa in Tokyo, and Matthew Lee in Washington contributed to this report.