More than 3,000 active duty troops will be joining the 2,300 who are already at the U.S. border with Mexico.

The extra troops were sent after a request for reinforcements from the Department of Homeland Security.

On Tuesday, acting Defense Secretary Patrick Shanahan told reporters that "several thousand" troops would be needed to beef up security at the border. CNN confirmed on Thursday through "several defense officials" that the number of the troops was in excess of 3,000.

The Pentagon said Jan. 14 that the DHS had requested more troops in order to assist with "mobile surveillance and detection, as well as concertina wire emplacement between ports of entry." That same day, the Pentagon announced that the U.S. military's mission to the U.S.-Mexico border, which would have expired on Thursday, would be extended through Sept. 30.

President Donald Trump tweeted on Thursday that the troops were being sent to "stop the attempted invasion of Illegals, through large Caravans, into our Country."

The DHS says that it is currently "tracking" three separate caravans heading to the U.S. border. One of these "is over 12,000 people in the latest estimate," according to Under Secretary of Defense for Policy John Rood.