The United States has called on North Korea not to take any further provocative actions after report of plans for more nuclear tests.
Friday's statement came after the North conducted its third nuclear test on Tuesday, drawing global condemnation.
Barack Obama, the US president, has pledged after this week's nuclear test "to lead the world in taking firm action in response to these threats" and diplomats at the UN Security Council have already started discussing potential new sanctions.
Meanwhile, North Korea's leader has made his first public appearance since Tuesday's controversial nuclear test.
Kim Jong-un handed out awards in memory of his late father Kim Jong-il to mark what would have been his 71st birthday.
Al Jazeera's Harry Fawcett, reporting from Seoul, said: "Kim Jong-il's birthday has been celebrated in a number of ways in the days leading up to it.
On Tuesday came the third nuclear test which was seen by many as timed to coincide with Kim's birthday.
"On Thursday there was a mass rally in Pyongyang in celebration of that achievement, and on Friday it was the first appearance of Kim Jong-un's since the tests, where he was giving out awards to members of North Korea's elites, scientists and technicians."
Further reports say that the North has told its key ally, China, that it is prepared to stage one or even two more nuclear tests this year in an effort to force the US into diplomatic talks with Pyongyang, a source told Reuters news agency.
The tests will be undertaken, the source said, unless the US holds talks and abandons its policy of what North Korea sees as attempts at government change.
North Korea also reiterated its long-standing desire for the US to sign a final peace agreement with it and establish diplomatic relations, he said.
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North Korea's latest test, its third since 2006, prompted warnings from the US and others that more sanctions would be imposed on it.
The UN Security Council has only just tightened sanctions on the North after it launched a long-range rocket in December.
The country is banned under UN sanctions from developing missile or nuclear technology after its 2006 and 2009 nuclear tests.
North Korea worked to ready its nuclear test site, about 100km from its border with China, throughout last year, according to commerciall available satellite imagery.
The images show that it may have already prepared for at least one more test, beyond Tuesday's subterranean explosion.
Initial estimates of this week's test from South Korea's military put its yield at the equivalent of 6-7 kilotonnes, although a final assessment of yield and what material was used in the explosion may be weeks away.
The North remains technically at war with both the US and South Korea after the Korean war ended in 1953 with a truce.
Source: Al Jazeera and agencies