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The North Korean official, quoted by state news agency KCNA, said that Washington was "misleading public opinion" by saying the denuclearisation pledge resulted from sanctions and other pressure.
"The US is deliberately provoking [North Korea] at the time when the situation on the Korean peninsula is moving toward peace and reconciliation thanks to the historic north-south summit and the Panmunjom Declaration," the statement said.
"This act cannot be construed otherwise than a dangerous attempt to ruin the hard-won atmosphere of dialogue and bring the situation back to square one.
"It would not be conducive to addressing the issue if the US miscalculates the peace-loving intention of [North Korea] as a sign of 'weakness' and continues to pursue its pressure and military threats against the latter."
This latest statement is a reminder that discussions between the two countries will not be easy, says BBC Asia editor Michael Bristow.