South Korea has raised its military alert level to the second highest category - the government there says it expects North Korea will launch a test missile "any day".
The Pacific Island of Guam has raised its official threat level and has this morning tested its emergency alert system after warnings from North Korea identifying the island as a potential missile target.
A North Korean missile test is expected at any time.
Authorities say the the US territory is on yellow alert, the middle phase of a three-step "traffic light" system. A government spokesman described the risk to the island as medium.
Washington has ordered two guided-missile destroyers to the Western Pacific - to bolster defences.
US Defence Secretary Chuck Hagel says Pyongyang is "skating very close to a dangerous line":
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