North Korea has said it is taking "practical measures" to strengthen its nuclear "deterrent" because diplomacy over its nuclear programme has failed.
North Korea restarted its Yongbyon nuclear reactor last year
A North Korean foreign ministry spokesman said the country was no longer interested in holding negotiations on the issue with the United States.
His comments came as high-level delegates from the US, Japan and South Korea met in Tokyo to discuss the crisis.
The nuclear standoff began in October 2002, when the US accused Pyongyang of processing uranium in defiance of a 1994 accord.
North Korea did not clarify exactly what "practical measures" it was considering.
But the foreign ministry spokesman told North Korean radio: "The request of one party to the conflict in asking the other party to come out with its hands up in the air is irrational thinking that nobody can accept."
"If such a unilateral demand by the United States is what is meant by a peaceful resolution, the only thing that it will summon will be war."
Since the start of the crisis, tensions have mounted, with six-nation talks on the issue ending inconclusively last month in Beijing.
Diplomats are currently working to arrange a new round of talks.
In Tokyo, US Assistant Secretary of State James Kelly, South Korean Deputy Foreign Minister Lee Soo-hyuck and their Japanese counterpart, Mitoji Yabunaka, met for their second day of discussions on the nuclear crisis.
Asked by reporters when the next round of talks with North Korea might be, Mr Kelly simply replied: "We don't know."
As the nuclear impasse with the North continues, so too does the collaboration between the United States and South Korea.
On Tuesday, the two countries marked the 50th anniversary of a mutual defence treaty, which was signed shortly after the end of the Korean War in 1953.
Washington still keeps 37,000 troops in South Korea as a result of the treaty.
"Unfortunately, one of the things that has survived in the last
50 years is the threat from North Korea," US ambassador to Seoul, Thomas Hubbard, said at a ceremony to mark the anniversary.
"Even as we pursue multilateral diplomacy to resolve peacefully the North Korean nuclear problem... our two countries must continue to maintain our strong combined deterrence against
the North Korean threat," he said.
As part of their mutual collaboration, the US has asked South Korea to send troops to help in peacekeeping operations in post-war Iraq.
But the National Security Council in Seoul said on Tuesday that the security situation on the Korean peninsula would be a "fundamental factor" in deciding whether to comply with the American request.