The official media in Pyongyang made the accusation on Saturday as Washington reiterated its call for multilateral talks to resolve the standoff over North Korea's suspected nuclear programme.
"It is quite clear these dangerous military moves being staged by the US behind the scene of 'multilateral talks' are aimed to mount a surprise attack on the DPRK (North Korea)," the Korean Central news agency, KCNA said.
"In case the US mounts a preemptive attack on it, the DPRK will take self-defensive measures involving all means equivalent to what the US will use," it added.
The US and South Korea agreed in June to gradually reposition US forces away from the Demilitarized Zone (DMZ) separating the two Koreas.
It was one of the biggest realignment of forces there since the Korean War in the 1950s, and part of a US move to redeploy its forces around the world.
The North Korean accusation came a day after Washington told a Chinese envoy it was time for other parties to join them in talks with North Korea to end Pyongyang's weapons programme.
State Department spokesman Richard Boucher said: "The US made clear our strong belief that the time has come for other parties to join the multilateral talks in order to ensure that all key issues are addressed."
The United States wants to expand the talks to include its east Asian allies, South Korea and Japan.
North Korea has been insisting on bilateral talks with the US, but it did agree to the three-way Beijing meeting in April.
A US official said on Wednesday North Korea seemed ready to restart the three-way talks - apparently dropping for now its demand for direct bilateral talks with the US.
"They (the Chinese) seem to have convinced the North Koreans that they have to accept the idea of multilateral talks; and if that's the case, that's obviously a big change," the senior Bush administration official said.
The North Korean nuclear crisis erupted in October when US officials said Pyongyang admitted to a clandestine atomic weapons programme.