North Korea has warned it will strengthen its nuclear deterrents in response to growing pressure from the United States.
The US' Colin Powell said the crisis was a matter of urgency
The statement by the North Korean Foreign Ministry, carried by KCNA news agency, also warned of retaliation in the event of any "hostile act".
State media earlier on Wednesday said the regime would never abandon its nuclear weapons programme without concessions from Washington.
The statements came as the US Secretary of State, Colin Powell, urged South East Asian ministers at a regional security forum in Cambodia to exert more pressure on Pyongyang to abandon its nuclear weapons programme.
"This is not a bilateral matter between the United States and
North Korea," Mr Powell told the Asean (Association of South East Asian Nations) Regional Forum, according to the French news agency AFP.
"It affects every nation in the region that would fall under the arc of a North Korean missile.
"Thus it must be solved as a multilateral problem," he said.
During Wednesday's talks, Mr Powell met briefly with North Korea's envoy to the Asean forum, and urged him again to agree to multilateral talks to end the eight-month nuclear impasse.
Analysts say Washington is reluctant to enter into another bilateral agreement with Pyongyang, after the collapse of a 1994 deal last year.
But, although neighbouring Tokyo and Seoul have both hardened their positions on the North, North Korea's main ally, China, is more reluctant to pressurise its fellow Communist state.
"We believe, of course, there should be no nuclear arms on the peninsula, it should be nuclear free," Chinese Foreign Minister Li Zhaoxing said at the ARF.
"At the same time of course, the DPRK's (North Korea's) security concerns should be appropriately addressed," he said.
Any collapse of the North Korean regime would mean that China's border could be flooded with hundreds of thousands of hungry North Koreans.
The DPRK will put further spurs to increasing its nuclear deterrent force for self-defence, as a just self-defence measure to cope with the US strategy to isolate and stifle
The main sticking point, however, is Pyongyang's refusal to enter into multilateral talks.
Pyongyang reiterated on Wednesday in a commentary in the state-run newspaper Rodong Sinmun that it only wants to discuss the issue with Washington.
"The US insistence on 'multilateral talks' is aimed to lay an international siege to the DPRK under the signboard of 'dialogue' and stifle the DPRK by force," the paper said.
"It is quite clear that the DPRK (North Korea) can never accept the US demand that it scrap its nuclear weapons programme first," it added.
Later, a statement by an unnamed Foreign Ministry official said: "The DPRK will put further spurs to increasing its nuclear deterrent force for self-defence, as a just self-defence measure to cope with the US strategy to isolate and stifle the DPRK."
Pyongyang has responded angrily to plans by a US-led initiative, announced this week, to step up international checks on North Korean ships.
And last week, officials from the US, South Korea and Japan met in Hawaii to co-ordinate policy on the North's nuclear threat.
It is unlikely that North Korea can address its simmering concerns with the US on Wednesday. Pyongyang only sent its ambassador to the Phnom Penh meeting, rather than its foreign minister.
The crisis on the Korean peninsula erupted in October last year, when the US revealed that Pyongyang had admitted to running a secret nuclear weapons programme based on highly-enriched uranium.
The US withdrew aid shipments under a 1994 deal designed to stop North Korea from developing nuclear arms. North Korea responded in December by withdrawing from the Nuclear Non-Proliferation Treaty.
Last week, Rodong Sinmun said Pyongyang was ready to build a nuclear deterrent.
And US officials at talks in Beijing in April said that the North Koreans told them privately that Pyongyang already has nuclear weapons and plans to build more.
The other issue dominating the one-day Asean Regional Forum was Burma's detention of its opposition leader, Aung San Suu Kyi.
Addressing the gathering of foreign ministers in Phnom Penh, Mr Powell said Burma's neighbours must step up the pressure against the country's junta to release her.
Asean took the unprecedented step on Tuesday of pressing its member state to free Aung San Suu Kyi from "protective custody", but fell short of taking action against its neighbour.