"We're not going to dignify North Korean comments about our undersecretary of state," spokesman Philip Reeker said.
North Korea's official news agency vilified Undersecretary of State John Bolton after he characterized North Korean Chairman Kim Jong Il as a "tyrannical dictator" in a speech last week to a gathering in South Korea.
Defending Bolton's speech, Reeker said it contained "obvious truths."
The verbal clash came despite movement toward talks on the Korean nuclear standoff.
North Korea and the United States announced last Friday that they had agreed to hold multilateral talks, which will include the two Koreas, the United States, Japan, China and Russia.
North Korea said Monday that the talks will begin "soon" in Beijing, while a South Korean official said they would begin early next month.
Pyongyang agreed to the six-way meeting after saying for months that it would only consent to bilateral talks with the United States. The North says it will work on the sidelines of the negotiations to push for one-on-one talks with Washington, which has insisted on multilateral talks because it says the North's nuclear program is a regional concern.
The nuclear standoff began in October, when U.S. officials said North Korea acknowledged having a uranium-based nuclear weapons program. That led the United States to cut off fuel shipments to North Korea that had operated under a 1994 deal halting the North's nuclear development.
Pyongyang subsequently threw out international inspectors and vowed to begin reprocessing spent fuel rods into bomb-making plutonium. In a series of public boasts and private statements to envoys in the ensuing months, North Korea has said that it has nearly completed that reprocessing, although U.S. intelligence could not confirm it.
The last time the United States and North Korea had official talks was in April in Beijing. U.S. officials said that North Korea claimed at the talks it already had nuclear bombs and planned to build more.
U.S. officials believe North Korea already has one or two nuclear bombs and can yield enough plutonium from its 8,000 spent nuclear fuel rods to build several more within months. There are also indications the North is preparing for some kind of nuclear test.
Since agreeing to the talks, North Korea has taken a two-pronged public relations approach.
According to The New York Times, Pyongyang has made moves to soften its image in Japan and South Korea.
At the same time, the tough talk toward the United States and its perceived allies has continued. On Saturday, the North warned that any moves to discuss its suspected nuclear weapons programs at the United Nations would "hamstring" efforts for dialogue and be a "prelude to war."
North Korea accuses the United Nations of siding with the United States to stifle it and fears the world body may impose economic sanctions on the impoverished communist nation.
China, the North's closest ally and a permanent member of the Security Council, had thwarted previous U.S. attempts to have the council condemn the North over its nuclear ambitions.
In his speech last week, Bolton criticized the Security Council, saying its credibility was at stake because it had failed to take up the North Korean nuclear issue.
According to press accounts, Bolton also said in his speech that, while North Korean leader Kim lived in luxury, "hundreds of thousands of his people locked in prison camps with millions more mired in abject poverty, scrounging the ground for food. For many in North Korea, life is a hellish nightmare."
On Tuesday, the North Korean news agency also said North Korea would not accept Bolton as a member of the U.S. team that will take part in the upcoming talks.
"The president and the secretary of state will choose the U.S. delegation," Reeker said.
In the past, Bolton has clashed with intelligence officials over his characterizations of alleged weapons of mass destruction in other countries.
Last month, The New York Times reported that the CIA had blocked Bolton from telling Congress that Syria's biological and chemical weapons programs were a danger to the region. The intelligence agency disagreed with the assessment.
In June, an intelligence analyst, Christian Westermann of the State Department's Bureau of Intelligence and Research, told the Senate Intelligence Committee that he had felt pressure from Bolton after the two disagreed over whether Cuba had a biological weapons program.
Bolton said last year that the U.S. believed Cuba had such a program.