North Korea "is fully ready to decisively control a pre-emptive nuclear attack with a strong retaliatory blow," the communist nation's Rodong Sinmun newspaper said in an English-language commentary carried by the state Korean Central News Agency.
At six-nation talks in Beijing on Monday, North Korea promised to give up its nuclear weapons program in return for economic aid and security assurances.
Since then, however, the North's rhetoric has underscored its unpredictability and cast doubt on its commitment to the accord hammered out with China, Japan, Russia, South Korea and the United States after four rounds of contentious negotiations stretching over two years.
North Korea said Tuesday it would not dismantle its atomic arms program unless Washington agreed to supply light-water nuclear reactors for generating electricity — a condition the U.S. government has already rejected.
Despite the tough statements, none of the North's negotiating partners said they expected a breakdown in the disarmament talks, which are scheduled to resume in November when the parties meet in the Chinese capital to begin the hard work of implementing the agreement.
Washington has repeatedly denied North Korean allegations of a planned attack, most recently in the joint statement at the talks in Beijing, where the U.S. delegation "affirmed that it has no nuclear weapons on the Korean Peninsula and has no intention to attack or invade (North Korea) with nuclear or conventional weapons."
Pyongyang and Washington also pledged to respect each other's sovereignty and to take steps to normalize relations.
The North demanded at the outset of the Beijing talks last week that it be given a light-water nuclear reactor — a type less easily diverted for weapons use — in exchange for disarming.
U.S. officials opposed the idea, maintaining North Korea could not be trusted with any type of nuclear program in light of its efforts to obtain atomic weapons.
The disarmament agreement sidestepped the issue, with participants saying they would discuss it "at an appropriate time."
North Korea's negotiating partners made clear the reactor could only be discussed after Pyongyang carries out the pledge it made Monday to rejoin the global Nuclear Nonproliferation Treaty and accepts inspections by the International Atomic Energy Agency.
Separately, a U.S.-led international energy consortium plans to meet Monday to discuss its suspended project to build two power-generating nuclear reactors in the North, said South Korean official Ryu Jin-young.
The reactors were meant as a reward to the North for agreeing with the United States in 1994 to freeze — and ultimately dismantle
its nuclear program. The $4.6 billion project was suspended in 2003 when U.S. officials said North Korea revealed it was still working on atomic weapons.