The Hawaii Army National Guard has been told to prepare around 1,000 soldiers for deployment to the Middle East and Europe next spring.
The warning comes after North Korea threatened to launch a missile strike against the island of Guam, a US territory in the western Pacific. Pyongyang's rhetoric followed US President Donald Trump's warning on 8 August that any threats to attack the US would be "met with fire and fury".
Six units of the Hawaiian army were given the orders on Thursday (10 August), just one day after tensions between the US and North Korea escalated. The soldiers would not be sent to Asia, reports said.
"It's possible that some of these units may not get mobilised," said Hawaii National Guard spokesman Lt. Col. Chuck Anthony.
Last month, Hawaii lawmakers called on emergency officials to update plans dating back to the Cold War on how to cope with a nuclear attack. The state's Emergency Management Agency (EMA) said preparations for a potential attack could not wait any longer.
"We do not want to cause any undue stress for the public ... but there is clear evidence that North Korea is trying to develop ballistic missiles that could conceivably one day reach our state," the EMA said in a statement after North Korea carried out its first successful test of an intercontinental ballistic missile (ICBM) in early July.
If the deployment goes ahead, it would be the largest mobilisation of Hawaiian troops in a decade. The last time the island deployed so many soldiers was towards the end of the Iraq war in 2009.