In a statement carried by KCNA news agency, the top military body said the "high-level nuclear test" and more long-range rocket launches were aimed at its "arch-enemy", the US.
The statement gave no time-frame for the test. North Korea has conducted two nuclear tests, in 2006 and 2009.
The move comes two days after a UN Security Council resolution condemned Pyongyang's recent rocket launch.
The Security Council also expanded sanctions against the communist country following its December launch, which was seen by the US and North Korea's neighbours as a banned test of long-range missile technology.
North Korea said the rocket put a satellite into space.