The defense officials described the force DHS requested as something that would only be used if CPB personnel were overwhelmed by the situation on the border.
Manning's statement came in response to comments by Air Force Gen. Terrence O'Shaughnessy that some of the troops being sent to the border will be armed.
By Monday, some 4,800 active-duty troops had arrived at the 13 logistics hubs that the Pentagon established to support the mission.
Secretary of Defense Jim Mattis is sending up to 5,200 troops to the border to defend it from the onslaught of migrants trying to cross into the country.
"We're not going to put up with that", Trump said during a White House press conference. "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". "But we're going to arrest those people quickly and for a long time".
However, ABC News has learned that the Department of Homeland Security (DHS) had made an initial request to the Pentagon "to hold" migrants seized along the border in tent structures, according to a US official. DHS officials have said that they are anxious that caravans of Central American asylum-seekers pushing up from the south may overwhelm CBP personnel.
President Donald Trump told supporters at a Montana rally on Saturday that the barbed wire installed by active-duty troops deployed to the U.S. -Mexico border this week was "beautiful". There are reports that this deployment could cost upwards of $200 million.
Manning also pointed out that soldiers "do not plan to interact with the protesters or migrant" at the border.
One US official cautioned that a previous Trump administration request dating back to the spring for national guard troops to build facilities for migrants on military bases was still being deliberated.
There are roughly 2,700 active-duty troops in Texas, 1,200 in Arizona and 1,100 in California, the Department of Defense revealed Monday.
Manning noted that DHS had requested that active duty troops, rather than reservists - who usually partake in operations on U.S. soil - for this operation.