North Korea has been filmed by spy satellites moving missiles into position before a potential clash with the US.
Senior US officials have told media that DPRK mobile missile launcher movement has been observed - a sign that an intermediate-ballistic missile launch may be coming.
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North Korea's leader Kim Jong Un has also received a report from his army on its plans to strike the area around Guam and says he will watch the actions of the US for a while longer before making a decision, the North's official news agency says.
"The United States, which was the first to bring numerous strategic nuclear equipment near us, should first make the right decision and show through actions if they wish to ease tensions on the Korean peninsula and prevent a dangerous military clash," Kim was cited as saying in the report by KCNA on Tuesday.
The North's leader ordered the army should always be fire-ready should he make a decision for action, the report said.
The comments come after US Defence Secretary Jim Mattis said the United States would know the trajectory of a missile fired by North Korea within moments and would "take it out" if the missile looked like hitting the US Pacific territory of Guam.
US officials and South Korea's president in recent days have played down the risk of an imminent conflict after Washington and Pyongyang exchanged fiery rhetoric last week.
But Mr Mattis told reporters on Monday that war could break out if North Korea were to fire a missile at the US.
"If they fire at the United States, it could escalate into war very quickly," he said.