Defence Secretary James Mattis is expected to deploy around 800 troops to the US-Mexico border to stop a migrant caravan, US media say.
The soldiers would assist with fencing and support at key points along the southern border, administration officials tell CNN.
The caravan of thousands of Central American migrants is making its way toward the US through Mexico.
President Donald Trump said on Thursday he was "bringing out the military".
"I am bringing out the military for this National Emergency," Mr Trump said of the migrant caravan in a tweet, hinting of an upcoming deployment. "They will be stopped!"
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