North Korea says it is "carefully examining" a plan to strike the US territory of Guam with missiles.

The threat came hours after President Donald Trump told Pyongyang that any threat to the US would be met with "fire and fury".

A spokesman for the Korean People's Army said the strike plan will be "put into practice in a multi-current and consecutive way any moment" once Kim Jong Un makes a decision.

He added that "enveloping fire" would be used to contain major US military bases on the island territory in the western Pacific Ocean - including the Anderson Air Force Base.

KCNA, Pyongyang's state-run news agency, also carried a statement from a different military official which said North Korea may carry out a pre-emptive operation if the US shows signs of provocation.

Guam's governor, Eddie Calvo, has said there is no change in the territory's threat level, and has reassured locals that several layers of defence are strategically placed to protect it.

He added that Guam is "not just a military installation" - but American soil with American citizens.

Earlier on Tuesday, the Washington Post had reported that North Korea has successfully made a miniaturised nuclear warhead that can fit inside one of its intercontinental ballistic missiles.

The newspaper said that claim was contained in a confidential assessment by America's Defence Intelligence Agency.

On Monday, North Korea responded angrily after the UN imposed tough new sanctions on the isolated state following the test firing of intercontinental ballistic missiles.

Pyongyang said the sanctions were caused by a "heinous US plot to isolate and stifle" the country - and its officials also threatened to make America "pay the price for its crime... thousands of times".