The threat came hours after US President Donald Trump threatened Pyongyang with "fire and fury" over its missile program and days after the UN Security Council levied new sanctions on North Korea over its growing nuclear arsenal.
Pyongyang said it's "now carefully examining the operational plan for making an enveloping fire at the areas around Guam with medium-to-long-range strategic ballistic rocket Hwasong-12," according to the official Korean Central News Agency (KCNA).
The plan will be finalised "and will be put into practice in a multi-concurrent and consecutive way any moment once Kim Jong-un, supreme commander of the nuclear force of the DPRK, makes a decision," it added.
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The threat came after Trump issued an apocalyptic warning, saying North Korea faces "fire and fury" over its missile program, after US media reported Pyongyang has successfully miniaturised a nuclear warhead.
Trump's warning followed a Washington Post report that quoted a Defense Intelligence Agency analysis as saying officials think North Korea now has "nuclear weapons for ballistic missile delivery" -- including in its intercontinental ballistic missiles.
The progress suggests North Korea is further along the path to having a deployable nuclear missile than had previously been acknowledged.
Australian prime minister Malcolm Turnbull said: “The North Korean regime's conduct is as illegal as it is reckless. It threatens the peace and stability of the region and the world, and they have to come to their senses.
“Every economic pressure that can be imposed must be imposed and Australia is playing its part. While every nation should be united in bringing this rogue regime to its senses, we note especially the importance of China's role as North Korea's major economic partner, China has unique leverage.
“And we welcome, in particular, China's support for these strong and much-more harsh sanctions imposed by the Security Council. The regime must come to its senses and stop its illegal provocations.”
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How serious is North Korea's nuclear threat?
Experts had until last month said it would take another two or three years for North Korea to develop a nuclear-tipped ICBM. But that calculus suddenly changed after Pyongyang last month tested two ICBMs -- the first time North Korean leader Kim had demonstrated such a capability.
The remarks mark a sharp rise in rhetoric from the United States. Previous administration comments have focused on finding non-military solutions.
North Korea has vowed that tough new UN sanctions agreed over the weekend would not stop it from developing its nuclear arsenal, rejecting talks and angrily threatening retaliation against the United States.
Technical hurdles
Despite the advance, North Korea still must overcome technical hurdles before it can claim to have perfected its nuclear weapons technology.
After Kim's second ICBM test, experts said it appeared the "re-entry vehicle" that would carry a warhead back into Earth's atmosphere from space had failed.
Without proper protection during a re-entry stage, a missile's warhead would burn up.
"North Korea likely made some of the key measurements required to define those extreme conditions during the two July tests, but I can't imagine it has learned enough to confidently make a warhead that is small and light enough and sufficiently robust to survive," Stanford University expert Siegfried Hecker said in an interview with the Bulletin of the Atomic Scientists.
The former Los Alamos National Laboratory director said he did not think North Korea yet has sufficient missile or nuclear test experience "to field a nuclear warhead that is sufficiently small, light and robust to survive an ICBM delivery."
News that Kim appears to have produced a small nuclear warhead comes as international tensions flare around Pyongyang's program.
"Especially since last year, when it pushed ahead with two nuclear tests and launched more than 20 ballistic missiles, it has posed a new level of threat," Japan's defense ministry said in an annual report.
North Korea has vowed that tough new UN sanctions agreed over the weekend would not stop it from developing its nuclear arsenal, rejecting talks and angrily threatening retaliation against the United States.
