The service members on the border "know exactly what they are doing, they know why they are doing it and they have the proper training and equipment to do it", he said.
"There is no plan for USA military forces to be involved in the actual mission of denying people entry into the United States", Dunford said.
The "priority" of this operation, Manning said, was to reinforce the entry points of the country and to locate key weak points at the border. "We have a problem with illegal immigration and the problem is that the Democrats will not allow us to change the dumbest laws in the history of the world on immigration".
"The requests that we have from the Department of Homeland Security and CBP (Customs and Border Protection) is to build (facilities) to support CBP personnel and our military personnel", he said.
By voicing its opposition, the Pentagon helped ensure that its mission was tailored to only providing support to USA government personnel on the border, US officials said. But they do that with us, they're going to be arrested for a long time.
Trump has been very vocal about the caravan, calling it an "invasion" and saying it will be met by the military.
The cost of mobilizing all those troops is estimated to be around $220 million.
Manning also pointed out that soldiers "do not plan to interact with the protesters or migrant" at the border.
US workers are photographed during construction of 32km of the border wall by order of US President Donald Trump on the border between Ciudad Juarez, Chihuahua state, Mexico and Santa Teresa, New Mexico state, US, on April 17, 2018.
When questioned on the cost of the operation on Monday morning Pentagon spokesman Col Rob Manning said, "I don't have a cost estimate for you, the Department will absorb the cost".
Manning noted that DHS had requested that active duty troops, rather than reservists - who usually partake in operations on USA soil - for this operation.