North Korea will stay away from talks on its nuclear programme for an "indefinite period", according to the nation's foreign ministry.
North Korea is believed to have built a handful of nuclear weapons
Pyongyang said there was no point in the talks since the US had termed North Korea an "outpost of tyranny".
The North also repeated a claim to have built nuclear weapons for self-defence.
But US Secretary of State Condoleezza Rice said the communist state would only deepen its international isolation if it pulled out of the talks.
"The world has given them a way out and we hope they will take that way out," she said at a news conference with European Union leaders.
Washington and Pyongyang have been locked in a diplomatic standoff since October 2002, when the US accused North Korea of operating an illegal uranium programme.
Since then three rounds of talks have been held - including China, Japan, Russia and South Korea - but little progress has been made.
The North Korean foreign ministry's statement, which was reported by state news agency KCNA, said: "We have wanted the six-party talks but we are compelled to suspend our participation... for an indefinite period".
It added that Pyongyang had "manufactured nukes for self-defence" and would take "a measure to bolster its nuclear weapons arsenal" in order to "protect its ideology, system, freedom and democracy".
This is North Korea's most explicit public assertion that it possesses nuclear weapons. Senior members of the regime have privately spoken about its nuclear capability on several occasions in the past.
US and other intelligence agencies believe the North could already have built a small number of weapons, variously estimated at between two and ten.
North Korea's anger appears to be directed at several keynote speeches made by US President George Bush and other senior members of his administration as they started their new terms in office.
"The second-term Bush administration's intention to antagonise the DPRK (North Korea) and isolate and stifle it at any cost has become quite clear," the statement said, citing the president's inaugural address and his State of the Union speech.
Condoleezza Rice's description of the isolated nation as an "outpost of tyranny" was also singled out for criticism.
US RHETORIC ON NORTH
19 Jan: Condoleezza Rice refers to North as an "outpost of tyranny"
20 Jan: No mention in George Bush's inauguration speech, though US goal was to "end tyranny in our world"
2 Feb: Mr Bush's State of the Union address says US working with governments in Asia to convince North Korea to abandon nuclear ambitions
"There is no justification for us to participate in the six-party talks again, given that the Bush administration termed the DPRK, a dialogue partner, an 'outpost of tyranny'," the statement said.
Some observers had hoped that Mr Bush's State of the Union speech would actually increase the chance of the stalled nuclear talks going ahead, because the president refrained from direct criticism of North Korea.
In a past speech, in 2002, he famously described Iraq, Iran and North Korea as part of an "axis of evil".
In Thursday's statement, Pyongyang also had strong words to say about Japan, which it described as "persistently pursuing its hostile policy toward the DPRK, toeing the US line".
It accused Tokyo of trying to prevent normalised relations by making false claims over the "abduction issue" - an ongoing row about missing Japanese nationals which North Korea admits to having kidnapped in the 1970s and 80s.
Pyongyang claims the issue has now been "settled".
Just hours before North Korea's statement was released, John Bolton, the US undersecretary of state for arms control and international security, said that Washington believed Pyongyang was still continuing to produce nuclear weapons.
"To whatever extent the North Koreans are proceeding with their programme, and we believe they are, the absence of progress in six-party talks means they are making further progress toward their increased capability," Mr Bolton told reporters during a visit to Tokyo.
"Time is not on our side," he added.