North Korea on Saturday condemned a port visit by a US aircraft carrier to the South as a "reckless" act of provocation following proposals by Pyongyang to ease cross-border tensions.
The USS George Washington arrived in the southern port of Busan on Friday for joint military exercises starting next week.
A spokesman of the Policy Department of the North's National Defence Commission (NDC) said the visit was "little short of its 'gunboat diplomacy' in the last century" and "in defiance" of the North's overtures.
"The US should properly understand that the more persistently it resorts to reckless nuclear blackmail and threat, the further the DPRK (North Korea) will bolster up its cutting edge nuclear force for self-defence", the spokesman was quoted as saying by the North's official Korean Central News Agency (KCNA).
He said the exercises, taking place after the North reached out last week, were an "open challenge" to its efforts.
"Whenever there was a sign of improving the north-south relations and detente on the peninsula, the US resorted to sinister interference and obstructions", he said in reference to the upcoming drills.
The George Washington is scheduled to take part in joint exercises with the South Korean navy from July 16-21 as part of annual military drills, Seoul's Yonhap news agency said.
It will then participate in a search and rescue exercise with South Korean and Japanese maritime forces in waters off the southern island of Jeju for two days starting July 21, it said.
Last week the NDC called for both the North and the South to halt all hostile military activities -- a suggestion Seoul dismissed as "nonsensical" in the light of Pyongyang's nuclear weapons programme.
North Korea issued another call Monday for a lowering of military tensions with South Korea, even as leader Kim Jong-Un oversaw firing drills on an island near the sensitive maritime border.
A government statement carried by KCNA said it was time to end "reckless hostility and confrontation" and called on Seoul to scrap its annual joint military drills with the United States.
South Korea has repeatedly made it clear that the annual joint drills are non-negotiable.