WASHINGTON (AP) - The Department of Defense is mobilizing more than 5,000 troops to 'harden' the United States' southern border this week.

The department said about 5,200 active duty troops are being sent to the border, the Associated Press reported. The order comes after President Donald Trump escalated his threats against a migrant caravan traveling to the border Monday, labeling the effort an "invasion" and declaring the "Military is waiting for you."

Trump tweeted about the caravan of several thousand Central American migrants moving through Mexico, saying no one will be admitted "unless you go through the legal process." Trump also said the group includes "Gang Members and some very bad people."

He has made similar claims before without offering evidence. The president has stepped up his focus on immigration in the days leading up to the midterm elections. The Pentagon last week approved a request for additional troops at the southern border.