North Korea says it is proceeding with plans for a third nuclear test.
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 North Korea's recent rocket launch.
The Security Council also expanded sanctions against Pyongyang 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.
The statement, which came from North Korea's National Defence Commission, hit out at the resolution as "illegal", before pledging a response.
"We do not hide that the various satellites and long-range rockets we will continue to launch, as well as the high-level nuclear test we will proceed with, are aimed at our arch-enemy the United States," KCNA quoted it as saying.
Reports suggesting North Korea could be preparing for a third nuclear test have been circulating for several weeks.
Earlier on Thursday, the South Korean defence ministry said it appeared that North Korea was "ready to conduct a nuclear test at anytime if its leadership decides to go ahead".
Regional neighbours and the US have urged it not to proceed.