The state-run Korean Central News Agency said U.S. interests are within reach of North Korean missile systems, adding the military is prepared to answer any aggression from U.S. or South Korean forces.
North Korea experts who spoke with Bloomberg News said Pyongyang's rhetoric may be premature.
"North Korea hasn't yet secured enough technology to strike the U.S. mainland," said Yang Moo-jin, who teaches at the University of North Korean Studies in Seoul.
The South Korean and U.S. governments agreed last weekend to extend the range of South Korean missiles to more than twice their current range of 500 miles. Seoul, Yonhap reports, aims to deploy its new ballistic missile system within five years.
Tensions on the Korean Peninsula escalated last year following the death of North Korean leader Kim Jong Il. Various analysts have suggested Pyongyang this year may be preparing for a nuclear test.
A spokesman for the North Korean military was quoted by Yonhap as saying Pyongyang was "well prepared to fight with nuclear (weapons)."