North Korea has moved missile equipment into position ahead of a possible launch, according to US defence officials.
American satellites detected the transportation of launchers capable of firing intermediate-range ballistic missiles (IRBMs) amid tension over threats by Pyongyang.
The movement is "not believed to be directly related to the threat issued by North Korea last week to strike the waters near Guam," a source told CNN.
But they added the activity was being "watched closely" by the US military.
It comes after James Mattis, the American Defence Secretary, warned a North Korean missile attack "could escalate into war very quickly".
He said the US would "take out" any such launch aimed at its territory, in an apparent reference to missile defence systems around Guam.
North Korean dictator Kim Jong-un said on Tuesday he would hold off on plans to fire four missiles towards the Pacific island and would instead "watch a little more the foolish and stupid conduct of the Yankees," according to a state news agency.
In photos released with the report, Kim was seen pointing at a map showing a flight path for the missiles from North Korea's east coast, flying over Japan towards Guam.
But the island's Homeland Security Adviser George Charfauros said the movement of missile launchers was likely "just a show of force" to mark the country's Liberation Day on Tuesday.
“It may be just a ruse. Today is an historic day for the Korean peninsular.... North Korea tends to use symbolism as part of their decision making," he said.
"There doesn't appear to be any indication, based on what we're hearing, that there will be any missiles attacking in the near future or in the distant future," Lieutenant Governor Ray Tonorio added.
Islanders were given a brief scare on Tuesday when two Guam radio stations accidentally broadcast an emergency danger warning for 15 minutes.
Listeners were warned of an unspecified threat at 12.25am local time.
Authorities stressed a real warning would describe the type of threat and said they were working with the stations to ensure the "human error" would not be repeated.
Tensions have been heightened on the island, home to 162,000 people and two military bases, since Pyongyang's threat last week.
But Mr Charfauros told residents to "remain calm", adding in a statement: "Remember there is no change in threat level, we continue business as usual and know there are US Department of Defence capabilities in place.
"We continue communication with our federal and military partners and have not received official statement warranting any concern for imminent threat to Guam or the Marianas.”
US President Donald Trump said last week his military was "locked and loaded" and ready to unleash "fire and fury" if North Korea acted "unwisely".
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