"We are now just referring to it as simply border support," Pentagon spokesman Lieutenant Colonel Jamie Davis said.

Davis did not provide a reason for dropping the name, but the change came over the last two days, during the final stages of this week's bitter midterm elections.

Critics had said President Donald Trump's order to send thousands of active-duty troops to the Mexican border was a political move to galvanize his voter base by drumming up fears of a migrant "invasion."

The Pentagon is traditionally apolitical. Last week, Defense Secretary Jim Mattis defended the decision to send thousands of soldiers to the border, rejecting criticism that the move was a political stunt.

"We don't do stunts in this department," he said.

Davis said there had been no changes to the mission, which could see about 9,000 active-duty and reserve troops working on or near the border.

The shift in the operation's name was first reported by The Wall Street Journal.