North Korea says it will consider continued pressure from the United States to be a declaration of war.
A statement carried by North Korea's official news agency, K.C.N.A., Wednesday, said Pyongyang will take "physical countermeasures" if Washington keeps pressing the government of Kim Jong Il over its nuclear program.
The U.S. has called for tough U.N. sanctions against North Korea, following Pyongyang's declaration Monday that it had tested a nuclear weapon.
North Korea's second in command, Kim Yong Nam, told Japan's Kyodo news agency Wednesday, Pyongyang could conduct more nuclear tests, if U.S. policy toward the country does not change. He said North Korea will return to six-party disarmament talks only if the U.S. lifts financial restrictions on Pyongyang.
Washington has long said those sanctions were imposed for alleged money laundering by North Korea and are a separate issue from the six-party talks.
The U.S. and other world leaders are calling for an immediate resumption of those meetings.
The United Nations Security Council will meet later Wednesday to discuss possible responses to the reported nuclear test. Among them are a total embargo on arms or bomb-making supplies bound for North Korea, a ban on luxury items and possible financial sanctions.
China's U.N. ambassador, Wang Guangya, says Beijing will support U.S. and Japanese demands for punitive measures, but that any punishment should be "appropriate."
Japanese media say Tokyo decided today to impose sanctions of its own on Pyongyang.
And South Korean media say the country's military is urging a prompt review of its preparedness for nuclear war. Military officials say a plan drafted by Washington and Seoul to respond to a North Korean threat may have to be revised to address a possible nuclear attack.
Pyongyang claims it tested a nuclear devise to bolster its defenses against U.S. aggression. U.S. Secretary of State Condoleezza Rice said Tuesday her country has no intention of invading or attacking North Korea.
It is still unclear what exactly caused the explosion in North Korea Monday.
U.S. intelligence experts say there are three possibilities. The first is that Pyongyang conducted a successful nuclear test. The second is that the test was a partial failure because it did not trigger a fission reaction and generate a true nuclear explosion. U.S. experts say the third and least likely possibility is that North Korea's announcement was a ruse, and that no nuclear materials were involved in the blast.
Some information for this report was provided by AFP, AP and Reuters.