The additions announced Sunday will bring the total number of active-duty troops on the border to 4,350.
Pentagon officials announced thousands more troops headed to the border just hours after a congressional hearing on the topic.
The announcement is in line with what Acting Defense Secretary Pat Shanahan had said on Tuesday when he provided estimates for the next phase of a military mission that critics have derided as a political ploy by the White House.
Shanahan said several thousand more troops would be sent mainly to install additional wire barriers and provide a large new system of mobile surveillance and monitoring of the border area. Sunday’s announcement said the mobile surveillance mission would last through Sept. 30.