The remark by an unnamed spokesman of North Korea's Foreign Ministry could be an indication that the communist regime intends to test a nuclear bomb. However, North Korea frequently makes belligerent statements without following up.
"When the time comes, the DPRK will take steps to physically display its nuclear deterrent force," the North Korean spokesman told Pyongyang's state-run news agency KCNA, which was monitored by the South Korean agency.
DPRK stands for North Korea's official name, Democratic People's Republic of Korea.
For weeks, North Korea has said that it was building up its "nuclear deterrent force," a term the isolated, communist nation uses to refer to its nuclear weapons program.
U.S. intelligence officials believe that North Korea already has one or two nuclear bombs and may be building more.
On Thursday, KCNA quoted the North Korean spokesman as saying his country has "no other option but to continue to take steps to keep and increase its nuclear deterrent force as a self-defense measure" because of what it calls U.S. plans to invade.
North Korea also accused the United States of stalling talks aimed at ending the year-old nuclear standoff.
Representatives from the United States, the two Koreas, China, Japan and Russia met in Beijing in August to discuss ways to end the crisis. The meeting ended without agreement on when to hold a next round talks, because of strident differences between Pyongyang and Washington.
North Korea demands that the United States sign a nonaggression treaty, provide economic aid and open diplomatic ties before it can dismantle its nuclear facilities.
Washington demands that North Korea first abandon its nuclear weapons program before any improvement in ties.
The nuclear dispute flared last October when U.S. officials said North Korea admitted running a secret nuclear weapons program in violation of international agreements.
The U.S. cut off fuel supplies, and North Korea kicked out nuclear inspectors and vowed to reprocess 8,000 rods into weapons grade plutonium.
The North said earlier this month that it had completed reprocessing the rods and had started using plutonium to make nuclear weapons as a deterrent against what it calls a U.S. plan to invade.
When reprocessed with chemicals, the 8,000 rods can yield enough plutonium to make five or six bombs, according to experts. American intelligence analysts believe North Korea already has at least one or two nuclear bombs.
The North has made similar claims about its nuclear capabilities since the crisis over its nuclear projects started a year ago. It was unclear whether the announcement was a sign North Korea has turned its back on the possibility of giving up its nuclear ambitions or was an attempt to gain leverage ahead of any talks on the matter.
Washington has said it has no intention of invading, but North Korea had demanded the U.S. sign a nonaggression treaty. Pyongyang claims to fear the United States because of President Bush's doctrine of preemptive war. Some analysts, however, speculate that impoverished North Korea is forcing a crisis to try to get more aid from the west.
So far, the U.S. has sought multiparty negotiations with North Korea. A nuclear test might challenge this approach, because Mr. Bush has said he will not tolerate a nuclearized Korean peninsula.