SEOUL — North Korea boasted Tuesday to running "thousands" of nuclear centrifuges, a week after launching a deadly artillery attack on South Korea, as China pressed for six-nation crisis talks.
State media in the North, which has already tested two atomic bombs made from plutonium, said "many thousands of centrifuges" are operating to enrich uranium at a new plant which it claims is for peaceful energy purposes.
The country first disclosed the new plant to US experts less than two weeks before its artillery assault, which killed two civilians and two marines on a South Korean island near the disputed Yellow Sea border.
Experts and senior US officials fear the plant could easily be configured to make weapons-grade uranium.
Analysts say the nuclear revelation and artillery attack appeared coordinated to pressure Washington and Seoul into resuming dialogue and aid, and possibly to bolster the credentials of the North's leader-in-waiting Kim Jong-Un.
For a third day, the US and South Korean navies staged war games far south of the border involving 11 ships, air power and 7,300 personnel.
South Korea is separately strengthening artillery and troop numbers on frontline islands near the tense frontier.
The North's state media blasted the naval drill, saying it was provocative and heightened the risk of war.
"We have full deterrence to destroy our enemies at once," said cabinet newspaper Minju Chosun. "If the US and South Korean enemies dare to fire one shell in our territory and sea territory, they will have to pay for it."
China's refusal publicly to condemn its ally for the shelling -- the first of a civilian area in the South since the 1950-53 war -- has stirred anger in South Korea.
And its call for talks to end the crisis has so far received a dismissive response from the United States and its Japanese and South Korean allies.
China Sunday suggested emergency consultations between envoys to the stalled six-nation talks on the North's nuclear disarmament.
"Under the circumstances it is imperative and important to bring the issue back to the track of dialogue and consultation as soon as possible," foreign ministry spokesman Hong Lei told reporters Tuesday.
"We believe parties concerned will take our proposal seriously and react positively."
The White House had said such talks would amount to "PR activity" unless Pyongyang changes its behaviour.
"The North Koreans need to demonstrate a seriousness of purpose in ending their aggressive behaviour," spokesman Robert Gibbs said Monday.
US ambassador Susan Rice urged tighter enforcement of UN sanctions in response to the "outrageous" artillery attack. China should play a "responsible leadership role" in defusing the crisis, she said.
Japan's foreign minister has also faulted China's proposal.
"It's unacceptable for us to hold six-party talks only because North Korea has gone amok," Seiji Maehara told the Wall Street Journal.
"We must first see some kind of sincere effort from North Korea, on its uranium enrichment programme and the latest incident."
South Korean President Lee Myung-Bak, in a toughly worded speech Monday, did not mention China's suggestion. But he said the North would not voluntarily mend its ways and promised to make it pay "a dear price" for any future attacks.
"We should recognise that (South Korea) is confronting the world's most belligerent group," he told a cabinet meeting Tuesday.
Almost 100 South Korean marine veterans landed on Yeonpyeong island Tuesday, vowing to defend it, ferret out spies -- and feed abandoned dogs.
"Execute Kim Jong-Il, Jong-Un," read a banner they erected after arriving by ferry, in reference to the North's leader and heir apparent.
With the nuclear disclosure and the bombardment, the North's leaders "demonstrated their ability to create trouble more or less with impunity", North Korea expert Andrei Lankov wrote in a commentary.
They "also hinted that they are not going to remain quiet if their demands for the resumption of unilateral aid and assorted political concessions are not met".
Diplomatic efforts were continuing, however.
Seoul's foreign ministry said its minister Kim Sung-Hwan would attend a Kazakhstan summit of the Organisation for Security and Cooperation in Europe on Wednesday and Thursday.
It said he was expected to meet US Secretary of State Hillary Clinton and Russian Foreign Minister Sergei Lavrov on the sidelines.
And two top North Korean officials arrived in Beijing on Tuesday, South Korean and Japanese media said.
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