He added: "The President has made it clear that border security is national security".
The extraordinary military operation comes a week before the November 6 midterm elections as Trump has sought to transform fears about the caravan and immigration into electoral gains. "We are going to hold them, we are going to build tent cities, we are going to build tents all over the place", he said, according to Agence France-Presse (AFP).
Republican lawmakers and other Trump supporters have applauded the deployment.
A Border Protection officer stands next to a recently completed section of the wall at the U.S. -Mexico border in Calexico, Calif., on Friday.
Troops planned to bring heavy concertina wiring to unspool across open spaces between ports.
There are about 2,000 USA troops deployed in Syria to combat Islamic State, according to the Pentagon. Some of the troops will be armed.
In April, Trump ordered up to 4,000 National Guardsmen to head to the border as a different migrant caravan wound its way north.
Additionally, officials were monitoring another group of about 3,000 people that had gathered at a border crossing between Guatemala and Mexico. The standoff at the riverbank followed a more violent confrontation on the border bridge over the river Sunday night, when the migrants threw rocks and used sticks against Mexican police. That group appeared to begin as a collection of about 160 who chose to band together in Honduras for protection against the gangs who prey on migrants traveling alone and snowballed as the group moved north.
Deputy foreign ministers from El Salvador, Guatemala, Honduras and Mexico met Tuesday and agreed to co-ordinate "special attention" for the caravan, guaranteeing human rights, humanitarian assistance and "a safe, orderly and regular migration" in accordance with each country's laws. A second group of about 3,000 migrants is at the border crossing between Guatemala and Mexico, he said. Under global law, these are considered refugees. "We're gonna have tents, they're gonna be very nice, and they're going to wait, and if they don't get asylum they get out".
O'Shaughnessy said the mission of what's being called Operation Faithful Patriot is to harden the border in preparation for the caravan of asylum-seeking migrant families making its way north through Mexico.
Trump steps up anti-immigrant offensive ahead of USA midterm vote
Trump ruffled several feathers when he announced that he wanted to issue an executive order to get rid of birthright citizenship .
The migrants rejected in a show of hands vote the offer for asylum, though organizers nor migrants elaborated on why they would keep traveling despite the offer.
But it doesn't sound as if the migrants want to stay in Mexico, a corrupt narcostate.
If an asylum seeker enters the USA illegally, they are still entitled to a hearing of their claim.
Previous presidents have ordered the military to support anti-drug smuggling operations and active-duty troops still do so. 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 new troops will include military police, combat engineers and helicopter companies equipped with advanced technology to help detect people at night.
US President Donald Trump in recent weeks has repeatedly said more troops are needed to tighten border security, and he has made political capital of the caravan ahead of crucial midterm congressional elections that could see the Democrats regain some degree of power. "It's going to be the election of common sense", Trump said at a rally in IL on Saturday night.
"Please go back", he urged them, "you will not be admitted into the United States unless you go through the legal process".
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. One migrant died after being struck by a rubber bullet in that area, Guatemalan firefighters have said.
Shaughnessy said the plan is to deploy the additional troops first to Texas and then to Arizona and California in support of U.S. Customs and Border Patrol.
The projected USA deployment is already roughly the same size as the US military contingent in Iraq.