The United States has announced it is moving an advanced missile defence system to the Pacific island of Guam as North Korea steps up its warlike rhetoric.
A statement from Pyongyang said its military had been given final approval to launch a nuclear strike.
North Korea has threatened to target the US and South Korea in recent weeks, following UN sanctions imposed after its latest nuclear test in February this year.
Its statement came amid warnings from US Defence Secretary Chuck Hagel that North Korea is a "real and clear danger" to America and its allies South Korea and Japan, the BBC reports.
Meanwhile, Pyongyang has again blocked South Korean access to the Kaesong joint industrial zone 10km inside North Korea. It was the second day the North had blocked the border crossing.
"Another statement from the North threatened to close the complex down "if the South's puppet conservative group and its media continue bad-mouthing [us]".
The US Department of Defense said on Wednesday it would deploy the ballistic Terminal High Altitude Area Defense System (Thaad) in the coming weeks.
The Thaad system includes a truck-mounted launcher, interceptor missiles and AN/TPY-2 tracking radar, together with an integrated fire control system.
The Pentagon said the missile system would be moved to Guam, a US territory with a significant American military presence, as a "precautionary move to strengthen our regional defence posture against the North Korean regional ballistic missile threat".
"The United States remains vigilant in the face of North Korean provocations and stands ready to defend US territory, our allies, and our national interests," it added.