The US has announced it is moving an advanced missile defence system to the Pacific island of Guam as North Korea steps up its warlike rhetoric.The latest statement from Pyongyang "formally informs" the Pentagon it has "ratified" a possible nuclear strike.
North Korea has threatened to target the US and South Korea in recent weeks.
Its latest statement came amid warnings from US Defence Secretary Chuck Hagel that North Korea is a "real and clear danger" to the US and its allies.
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.