North Korea 'crisis gone too far' says UN's Ban Ki-moon
UN chief Ban Ki-moon has said the North Korea "crisis has gone too far" after Pyongyang announced plans to restart its main Yongbyon nuclear complex.
Speaking at a news conference during a visit to Andorra, Mr Ban called for urgent talks with the North.
The move by Pyongyang is the latest in a series of measures in the wake of its third nuclear test in February.
North Korea has been angered by the resultant UN sanctions and joint US-South Korea annual military drills.
"Things must begin to calm down, there is no need for the DPRK [North Korea] to be on a collision course with the international community. Nuclear threats are not a game," Mr Ban said.
Earlier, a South Korean foreign ministry spokesman said that if true, the North Korean move - which includes reactivating a reactor mothballed for six years - would be "highly regrettable".
Chinese foreign ministry spokesman Hong Lei called for restraint from all sides to resolve the "complex and sensitive" situation.
Weeks of rhetoric and almost daily threats by the North have raised tensions on the Korean Peninsula to their highest levels for years.
Seoul and the US had warned of a "swift and strong response" to any military provocation.
White House spokesman Jay Carney said the decision to reopen the Yongbyon reactor was "another indication" of North Korea "violating its international obligations".
The US has urged China and Russia to apply pressure on Pyongyang to change its Yongbyon plans.
Russia's foreign ministry, meanwhile, warned against escalating tensions on the Korean peninsula.
"The main objective is to avoid the forceful military scenario. It is not acceptable to use the situation there (on the Korean peninsula) to try to reach someone's specific military and political aims," said ministry spokesman Grigoriy Logvinov.
The BBC's Lucy Williamson in Seoul says Yongbyon has provided the North with successful leverage in the past.
The complex offers Pyongyang two ways of making nuclear bombs - a uranium enrichment facility, and a nuclear reactor, from which the spent fuel can be turned into plutonium.
Restarting it gives the regime several cards to play: it secures more material for its nuclear programme, and also re-focuses world attention on how to stop it, our correspondent says.
The reactor at Yongbyon - which was the source for plutonium for North Korea's nuclear weapons programme - was closed in July 2007 as part of a disarmament-for-aid deal.
The cooling tower at the facility was later destroyed, but then the disarmament deal stalled.
Part of the reason the agreement fell apart was because the US did not believe Pyongyang was fully disclosing all of its nuclear facilities - a suspicion later bolstered when North Korea unveiled a uranium enrichment facility at Yongbyon to US scientist Siegfried Hecker in 2010.
While it appeared to be for electricity generation purposes, Mr Hecker said the facility could be readily converted to produce highly-enriched uranium for bombs.
In a November 2010 report following his visit to Yongbyon, Mr Hecker said based on what he saw he believed North Korea could "resume all plutonium operations within approximately six months" at Yongbyon if so inclined.