Despite this show of belligerence, Vice Foreign Minister Choe Su-hon said the isolated Communist state would not export its atomic capabilities.
His comments, reported by China's Xinhua news agency on Thursday, would mark a major step in North Korea's nuclear programme since the rods could provide plutonium to make fissile material and had been sealed under a 1994 agreement with the United States.
Choe played down the chance of a new round of international talks on his country's nuclear programme, but a senior South Korean official said Pyongyang was prepared to attend six-way talks and brushed off a string of comments to the contrary by Pyongyang as a diplomatic tactic.
North Korea had already "processed 8,000 fuel rods" and had "changed the purpose of these fuel rods", Xinhua quoted Choe as saying, although he gave no details as to the new purpose.
"We have no intention of transferring any means of that nuclear deterrence to other countries," Choe told reporters at the North's mission to the United Nations in New York.
The United States has been increasingly anxious about whether reclusive North Korea has a nuclear weapon since it said a year ago it possessed enriched uranium and this year expelled UN inspectors, pulled out of the nuclear Non-Proliferation Treaty and took its Yongbyon nuclear plant, where the rods are stored, out of mothballs.
US officials have voiced fears North Korea might try to export its nuclear technology and say it could already have one or two nuclear devices. If it has processed the fuel rods, that could give North Korea access to enough plutonium eventually to produce as many as five or six devices.
"One thing we can tell you is that we are in possession of nuclear deterrence and we're continuing to strengthen that deterrence"
N Korean Vice Foreign Minister
Choe refused to disclose the scale of Pyongyang's nuclear arsenal, Xinhua said. "One thing we can tell you is that we are in possession of nuclear deterrence and we're continuing to strengthen that deterrence."
Pyongyang "has no plan with regard to uranium enrichment", Choe said, but did not elaborate.
New talks in doubt
His remarks came as the United States and key Asian allies try to persuade Pyongyang to hold another round of six-way talks to resolve the tense deadlock.
Choe said his country had made no promises to participate in a second round of the talks, which also involve China, Russia, the United States, Japan and South Korea. The first round took place in Beijing in August.
"Certain mass media is circulating rumours as though we have just made promises to participate in the next round of the six-party talks," Choe said. "Unfortunately, this is not true."
However, US Assistant Secretary of State, James Kelly, Washington's pointman on North Korea, said this week the United States and its allies urging Pyongyang to return to the table and a round of talks in November was a possibility.
"North Korea is prepared to respond to six-way talks, and they are not in a position to oppose talks," South Korean Vice Unification Minister, Cho Kun-shik, told a briefing on Thursday.
Choe reaffirmed the North's stance that its nuclear programme was solely for self-defence.
"Since the United States has threatened the DPRK with nuclear weapons to launch a pre-emptive nuclear attack against the DPRK, we have no choice but to be in possession of the nuclear deterrence," Choe said, referring to the country by its official name, the Democratic People's Republic of Korea.
"That's why we have taken up all measures to maintain and strengthen that nuclear deterrence."