"This is an invasion of our Country", the commander in chief said, adding: "and our Military is waiting for you!"
Speaking to Fox News, Mr Trump said migrants would be housed in tents, rather than released, pending court decisions.
The president has stepped up his focus on immigration in the days leading up to the midterm elections.
"What I can confirm is there will be additional force over and above the 5,239".
Troops planned to bring heavy concertina wiring to unspool across open spaces between ports.
"They are incentivized to try to cross our border by the gaps in our legal framework and the expectation that they would be allowed to stay", said US Customs and Border Protection Commissioner Kevin McAleenan. Some of the troops will be armed.
Last week, U.S. Defense Secretary Jim Mattis authorized the use of troops and other military resources at the U.S-Mexico border.
Like the National Guard members who have been supporting CBP efforts at the border since April, the 5,200 deploying troops are not expected to interact with migrants. All of the active-duty troops are scheduled to be deployed by the end of the week, but some are already in the Rio Grande Valley.More news: Government Initiates Consultations With RBI Under Rare Provision
Mexico routinely complains about the treatment of its own citizens living in the U.S. without the proper papers, but has been detaining and deporting Central Americans in large numbers since 2014.
The caravan of migrants clash with the Guatemalan Police, in Tecun Uman, Guatemala. One of the riders died from a head injury although it is unclear how he sustained it. "It is going to be very little, compared to what they need".
Migrants hitch rides on passing truck as they continue on their journey after Mexican police briefly blockaded the road to keep them from advancing, outside the town of Arriaga, Mexico, Saturday, Oct. 27, 2018. Earlier this year, only about 200 from a caravan of some 1,000 migrants reached the Tijuana-San Diego frontier. Under global law, these are considered refugees.
Three helicopters will be deployed and enough barbed wire will be made available to cover 150 miles of the border.
We're relying on media reports from an area without a lot of security or reliable sources, so it's tough to say who is telling the truth here. More than 1,500 of the original group have applied for asylum in Mexico. "We want to work with Mexico to manage that flow".
The military operation drew quick criticism. We will, if necessary, to increase the number of military.
The US military is prohibited from carrying out civilian law enforcement on US soil unless specifically authorized by Congress. The troops will include military police, combat engineers and others helping on the border.
President Donald Trump, who has seized upon the Central American migrant caravan in campaign rallies ahead of the vote, said on Twitter that the military would be waiting for the procession - suggesting a far more direct role in confronting the migrants than USA defense officials have previously suggested. "It's going to be the election of common sense", Trump said at a rally in IL on Saturday night.
It's possible there are criminals mixed in, but Trump has not substantiated his claim that members of the MS-13 gang, in particular, are among them.
The Pentagon says it will send 5,000 USA troops to the border.