Pyongyang responded to UN criticism of its recent rocket launch
China and Russia have urged North Korea to reconsider its decision to abandon talks over its nuclear programme.
China, Pyongyang's closest ally, called for "calm and restraint" from all sides. Russia said it hoped talks would resume "very soon".
The US called North Korea's move a "serious step" in the wrong direction.
The North said it would walk out of talks and restore its disabled nuclear reactor following UN criticism of its recent rocket launch.
North Korea says its launch was part of a peaceful space programme, designed to put a satellite into orbit, but critics say it was a long-range missile test.
Six-party talks, involving North and South Korea, China, Japan, Russia and the US, have seen many setbacks since they began more than five years ago.
China and Russia appealed for the North to return to negotiations.
A Foreign Ministry statement said that Beijing hoped "all sides will... continue to advance and push forward the six-party talks and the denuclearisation of the Korean peninsula".
Moscow expressed regret at the North's decision.
- North Korea agrees to close its main nuclear reactor in exchange for fuel aid
- North Korea shuts its main Yongbyon reactor
- North Korea makes its long-awaited declaration of nuclear assets
- The US removes North Korea from its list of countries which sponsor terrorism
- Pyongyang slows work to dismantle its nuclear programme after a US decision to suspend energy aid
- The North says it is scrapping all military and political deals with the South, accusing it of "hostile intent"
5 April 2009
- Pyongyang launches a rocket carrying what it says is a communications satellite
14 April 2009
- After criticism of the launch from the UN Security Council, North Korea vows to walk out of six-party talks
"Despite the inevitable emotion from different sides in such a situation, we hope that the process of six-party talks will be resumed in the very near future," said Foreign Minister Sergei Lavrov.
The US, meanwhile, urged North Korea to end what it called "provocative threats" and abide by its obligations.
"North Korea will not find acceptance by the international community unless it verifiably abandons its pursuit of nuclear weapons," a White House spokesman said.
Japan, which had renewed unilateral economic sanctions against North Korea for another year because of its rocket launch, strongly urged Pyongyang to resume talks.
Earlier, North Korea had said a UN statement condemning its rocket launch and tightening existing sanctions was an "unbearable insult".
The statement infringed its sovereignty and "severely debases" its people, the North Korean foreign ministry said.
It said North Korea would "strengthen its nuclear deterrent for its defence by all means".
The North also said that it would restore its partially disabled Yongbyon nuclear reactor - the fuel source for its 2006 atomic test.
Pyongyang partially dismantled the Yongbyon plant in 2008, as part of an international agreement which guaranteed it aid and diplomatic concessions in exchange for disabling its nuclear facilities.
The BBC's diplomatic correspondent Jonathan Marcus says this latest instalment of the North Korean drama has been seen by many analysts as a predictable attempt by Pyongyang to gain the attention of the new US administration.
How far the North Koreans are really willing to go in unpicking the current deal is not clear, he says.
With growing uncertainty about the internal political dynamics in Pyongyang, and a much tougher sounding leadership in South Korea, it may not be easy to get these talks back on track, our correspondent says.
Pyongyang's defiant response came shortly after the 15-member Security Council unanimously condemned the long-range rocket launch on 5 April.
The council also ordered the UN Sanctions Committee to begin enforcing both financial sanctions and an existing arms embargo imposed after the 2006 tests.
There had been hope that the unified statement could pave the way for a return to the talks, which have stalled over the inability to verify the shutdown of Yongbyon.
North Korea had previously threatened that any criticism of the rocket launch would cause it to walk away from the negotiating table.