The Bush administration responded sternly, saying while it had no intention of attacking, it was determined to protect the United States if North Korea launched a long-range missile.
"Should North Korea take the provocative action of launching a missile the U.S. would respond appropriately, including by taking the necessary measures to protect ourselves," Julie Reside, a State Department spokeswoman, said.
Still, Reside said, the United States and other countries that have negotiated with North Korea are seeking a fundamentally different relationship with the reclusive regime. She said that relationship must be based on the complete and verifiable elimination of North Korea's nuclear weapons and nuclear program.
"We and our partners in the six-party process continue strongly to urge North Korea not to launch a long-range missile and, instead, to return to the six-party talks," she said in a statement.
The North's warning effectively stepped up its customary anti-U.S. vitriol, in which it often accuses Washington of plotting an attack. The North has recently come under heightened scrutiny after reports by the United States and Japan that it has taken steps to prepare for a test of a long-range missile.
The North's Korean Central News Agency, citing an unidentified "analyst" with the state-run Rodong Sinmun newspaper, accused the United States of harassing Pyongyang with war exercises, a massive arms buildup and increased aerial espionage by basing new spy planes in South Korea.
"This is a grave military provocation and blackmail to the DPRK, being an indication that the U.S. is rapidly pushing ahead in various fields with the extremely dangerous war moves," the dispatch said.
"The army and people of the DPRK are now in full preparedness to answer a pre-emptive attack with a relentless annihilating strike and a nuclear war with a mighty nuclear deterrent," the report said.
DPRK stands for the North's official name, the Democratic People's Republic of Korea.
The report concluded by urging the U.S. to "get out of South Korea promptly." About 29,500 U.S. troops are stationed in South Korea as a deterrent against the communist North.
On Friday, Pyongyang accused the United States of driving the situation on the Korean Peninsula "to the brink of war," and said it is fully prepared to counter any U.S. aggression.
Washington and Japan have said in recent weeks that spy satellite images show North Korea has taken steps to prepare a long-range Taepodong-2 missile for a test-launch.
Estimates for the range of the missile vary widely, but at least one U.S. study said it could be able to reach parts of the United States with a light payload.
Speculation that Pyongyang could fire the missile has waned in recent days, however, since the country's top ally and a major source of its energy supplies, China, publicly suggested North Korea should not to go ahead with the test.
A news report said Monday that China has offered a new proposal over the stalled six-party talks.
Chinese State Councilor Tang Jiaxuan told Ichiro Ozawa, the head of Japan's main opposition party, that China had relayed the proposal to Japan, the two Koreas, the United States and Russia, Kyodo News agency reported, citing party officials.
The report did not elaborate on the proposal. An opposition party spokesman in Tokyo could not be reached for comment. Ozawa is in Beijing for a six-day stay that party officials hope will include a meeting with Chinese President Hu Jintao, according to Kyodo.
The United States and its allies South Korea and Japan have taken quick steps over the past week to strengthen their missile defenses. Washington and Tokyo are working on a joint missile-defense shield, and South Korea is considering the purchase of American SM-2 defensive missiles for its destroyers.
The U.S. and North Korea have been in a standoff over Pyongyang's nuclear weapons program since 2002. The North claims to have produced nuclear weapons, but that claim has not been publicly verified by outside analysts.
While public information on North Korea's military capabilities is murky, experts doubt that the regime has managed to develop a nuclear warhead small enough to mount on its long-range missiles.
Nonetheless, Lt. Gen. Michael Maples, director of the Defense Intelligence Agency, told U.S. lawmakers last week that officials took the potential launch reports seriously and were looking at the full range of capabilities possessed by North Korea.