The federal agency says the caravan of people seeking asylum that's headed toward the Texas-Mexico border, with an unknown destination, will attract the attention of others. Trump tweeted on Thursday. No one at CBP, including the Border Patrol, endorses this activity.
The additional troops will not have any authority to apprehend illegal immigrants but will be able to erect barriers and provide reconnaissance searching for illegal border crossers.
KRGV's Christian von Preysing spoke with several property owners about the agency's efforts.
But four days after crossing into Mexico, the caravan is still more than 3,000 kilometers (1,860 miles) from the U.S. border.
The travel ban, announced shortly after Mr Trump took office, affected people from seven countries, five of them with Muslim majorities.
President Trump doubled down on his assertion that there are Middle Easterners and possible terrorists among the migrants in the caravan. Thousands of National Guard troops have been deployed there since April.
The White House is considering a major executive action to stop a massive caravan of Central American migrants traveling north through Mexico from entering the US, according to several reports on Thursday.More news: Trump calls Khashoggi's death 'worst cover-up in history of cover-ups'
The caravan is more than 1,000 miles south of the border, and it is unclear when or whether the migrants will arrive, and how many will seek to cross into the United States.
The US military is prohibited from carrying out civilian law enforcement on American soil unless specifically authorized by Congress.
The service personnel expected to be sent by the Pentagon will be a mix of active-duty or Reserve troops, Bowman adds.
They retain the right of self-defence, but border patrol officers will still be the ones physically stopping illegal migration.
In a tweet sent on Thursday, President Trump addressed the migrant caravan directly, advising them to follow the laws of the United States and apply to come in legally. Many are fleeing violence, poverty and government corruption in their home countries.
But Nielsen warned: "This caravan can not come to the United States".
One piece of the action under consideration would use an authority similar to that invoked by the travel ban, which would block entry to unauthorized immigrants who are not yet in the US, said the three sources. It's not yet clear if the Department of Homeland Security will reimburse the Pentagon. "The president should not be using the military to further a partisan agenda".
But Trump told a rally crowd in Wisconsin on Wednesday that moves were underway. "You're going to see a very secure border", he said.