The UN Security Council has agreed on a formal statement urging North Korea to cancel any planned nuclear test and return to disarmament talks.
Kim Jong-il has appeared being cheered at an army event
The final text unanimously adopted by the council expressed "deep concern" over the nuclear test threat made by Pyongyang on Tuesday.
The UN statement warned that such a test would lead to further unspecified Security Council action.
Some observers have warned that a test could come as early as this weekend.
KOREAN NUCLEAR CRISIS
Sept 2005:At first hailed as a breakthrough, North Korea agrees to give up nuclear activities
Next day, N Korea says it will not scrap its activities unless it gets a civilian nuclear reactor
US imposes financial sanctions on N Korea businesses
July 2006: N Korea test-fires seven missiles
UN Security Council votes to impose sanctions over the tests
Oct 2006: N Korea threatens nuclear test
The council statement said a nuclear test would "jeopardize peace, stability and security in the region and beyond" and "bring universal condemnation by the international community."
It said: "The Security Council will act consistent with its responsibility under the Charter of the United Nations."
"It was a very good statement," Russian Ambassador Vitaly Churkin told reporters. "We are pleased that it has been adopted."
"It is a very strong message in favour of respect for non-proliferation."
Japan's Vice-Foreign Minister Shotaro Yachi told Japanese TV after talks with US officials in Washington that it was possible a test could come this weekend.
The North's reclusive leader Kim Jong-il has appeared on state TV being cheered at an army event.
He was greeted with "stormy cheers of hurrah", the official KCNA news agency reported.
It did not say when he made his appearance, but it is the first to be reported in three weeks.
He congratulated military commanders for "bolstering" the country's armed forces and urged them to "further strengthen the battalions", KCNA said.
Japan said on Friday it was stepping up its monitoring of North Korea, although there was not thought to be any specific intelligence suggesting a test might take place this weekend.
"They will probably go ahead and do it as they had that tone in their declaration. It possibly means they are already very prepared," Mr Yachi said.