North Korea Friday promised more "self-defence" measures if the United Nations punishes the communist state with fresh sanctions over its nuclear test.

"If the UN Security Council provokes us, our additional self-defence measures will be inevitable," the foreign ministry said in a statement carried by official media.

Council members are trying to agree on additional sanctions against Pyongyang after it shocked the world by staging its second nuclear test on Monday.

"Any hostile acts by the UN Security Council will be tantamount to the demolition of the armistice," the ministry said in reference to the truce which ended fighting in the 1950-53 Korean War.

"The world will soon witness how our army and people stand up against oppression and despotism by the UNSC and uphold their dignity and independence."

It did not elaborate on what it would do but reiterated that Monday's test was a "self-defence measure."

Pyongyang had already said Wednesday it was no longer bound by the armistice and threatened attacks on South Korea, after Seoul announced it had joined a US-led initiative to halt the trade in weapons of mass destruction.

Complaining of double standards, the North said its nuclear test was the 2,054th in the world's history and that the Security Council's five permanent members had carried out virtually all of the previous tests.

"The North is sending a strong warning to the Security Council as it is likely to pass a resolution in the coming week," said Professor Yang Moo-Jin of Seoul's University of North Korean Studies.

"The North may put its military on a war footing, test-fire a long-range missile and restart the plutonium reprocessing facilities at Yongbyon," he told AFP.

"It may also start naval clashes in the disputed waters in the Yellow Sea, create trouble along the Demilitarised Zone or carry out mass military drills."

The North could also stage a third nuclear test but this would come much later than the other steps, Yang said.

The second test was assessed as about four times more powerful than the first in October 2006. --AFP