United Nations Secretary-General Ban Ki-moon says tensions involving North Korea have "gone too far," while the United States says Pyongyang is far from following through on its latest threat to restart an idle nuclear reactor.
Ban said Tuesday the North is on a "collision course" with the international community. The secretary-general said he is convinced no one intends to attack North Korea, and that negotiations are the only way to resolve the crisis.
In Washington, State Department spokeswoman Victoria Nuland said there is a "long way to go" for the North to be able to restart its Yongbyon plutonium nuclear reactor.
The North's official Korean Central News Agency (KCNA) said Tuesday Pyongyang plans to activate the complex to build more weapons and address the country's electricity shortage. It said the restart will include a uranium enrichment plant and a five-megawatt reactor that can produce weapons-grade plutonium.
The reactor was shut down in 2007 in exchange for economic aid.
Pyongyang's move to restart its nuclear complex comes days after North Korean leader Kim Jong Un pronounced that developing atomic weapons is one of the country's top priorities.
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South Korea's Foreign Ministry called the latest move "highly regrettable" and urged Pyongyang to abide by its international agreements.
China, North Korea's main ally, expressed "regret." A spokesperson, Hong Lei, repeated Beijing's call for all parties involved "to keep calm and exercise restraint."
Tensions Rising on Korean Peninsula
February 12: North Korea carries out third nuclear test
March 27: North Korea cuts military hotline with South Korea
March 28: U.S. B-2 bombers fly over Korean peninsula
March 30: North Korea says it has entered a "state of war" with South Korea
April 3: North Korea blocks South Korean workers from Kaesong
April 4: North Korea moves a missile to its east coast
April 9: North Korea urges foreigners to leave the South. The U.S. and South Korea raise alert level
April 14: US Secretary of State John Kerry offers talks with Pyongyang if it moves to scrap nuclear weapons
April 16: North Korea issues threats after anti-Pyongyang protests in Seoul
April 29: North Korea holds back seven South Koreans at Kaesong
April 30: North Korea sentences American to 15 years hard labor for hostile acts
May 20: North Korea fires projectiles for a consecutive third day
May 24: North Korean envoy wraps up China visit for talks on Korean tensions
June 7: South Korea accepts Pyongyang's offer of talks on Kaesong and other issues
“We have noticed the remarks of the DPRK and expressed our regret," said Lei. "It is the Chinese side's persistent position to realize denuclearization of the peninsula and protect peace and stability of the peninsula and northeast Asia."
North Korea agreed to halt operations at the plutonium-based reactor and destroy its cooling tower as part a 2007 aid-for-disarmament deal at the now-stalled six-party talks.
Mark Fitzpatrick, a senior analyst at the London-based International Institute for Strategic Studies (IISS), tells VOA his best guess, based on Western observers who have seen the facility, is that it would take about six months to get the reactor running again.
"We're not looking at an immediate production of plutonium, but once they get started, they would be down the path to expanding their nuclear arsenal," said Fitzpatrick.
KCNA says work will begin immediately on refurbishing the reactor. Nuclear scientists say it would take at least a year of restarted operations to generate enough plutonium to make one nuclear bomb. Pyongyang is currently believed to have enough plutonium to make up to eight bombs.
Fitzpatrick says it is less clear what to make of North Korea's threat to "restart and re-adjust" its uranium enrichment facility at Yongbyon. But he says the danger is that the facility, which was unveiled in 2010, could give Pyongyang an easier way to make nuclear weapons.
"Highly enriched uranium is also easier to conceal from observation," he said. "The enrichment can take place in small facilities that don't give off any obvious heat signature or any release of radiation unlike plutonium, which has to be produced in a reactor that is observable from the sky."
North Korea's first two nuclear tests, in 2006 and 2009, were carried out using plutonium. It is not yet known whether its latest test in February used plutonium or uranium.
North Korea, which is angry at tough U.N. sanctions passed in response to its third nuclear test and latest satellite launch, has been making threats for weeks. They include turning Seoul into a "sea of fire" and firing rockets at U.S. military bases in Hawaii, Guam and Japan.