The Pentagon says it will send 5,000 USA troops to the border.
The massive chain of migrants slowly making its way towards the US southern border, which is still some 1,000 miles north, is now demanding that the Mexican government provide transportation for its estimated 4,000 participants - demands issued amid reports of outbreaks of violence as more groups have forced their way through Mexico's southern border.
Trump says: "We're going to build tent cities".
"There could be incidental interaction between our military members and migrants and other personnel that may be in that area", he added, and to address that, "we are making sure our soldiers, our Marines are going to be fully trained on how to do that interaction - they are going to understand the rules for that interaction", The Hill reported.
Many basic questions remain unanswered a day after the Pentagon announced an open-ended deployment of over 5,200 active-duty troops to the border, including the cost and scope of the mission as well as the Pentagon's assessment of any threat posed by arriving migrants.
But Trump, who stoked anger and fear over illegal immigration on his way to winning the 2016 presidential election, has seized on the caravan at campaign rallies ahead of next week's midterm polls, hoping the issue will again fire up his core support. Around 2,000 National Guard troops have already been deployed to the border, with as many as 5,200 more active-duty troops poised to head that way if needed. There are already more than 2,000 National Guard troops providing assistance at the border.
On Tuesday, he stepped up his dire warnings, calling the band of migrants fleeing poverty and violence in Central America an "invasion". One migrant was killed Sunday night by a head wound, but the cause was unclear.
The US military is prohibited from carrying out civilian law enforcement on US soil unless specifically authorized by Congress.
"This will be the election of the caravans, the Kavanaughs, law and order, tax cuts, and you know what else?"
Trump said anyone wanting to get into the United States must do so through the legal process.
The Mexican government, according to the Associated Press, has shown little inclination to assist the caravan, with the exception of its migrant protection agency giving some of the caravan's stragglers rides to the next town over the weekend.
"Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border", Trump tweeted.
Anyway, blocking the progress of the train of unemployed "migrants" is only a temporary measure apparently, AP reported: "A standoff unfolded as federal police officers blocked the highway, saying there was an operation underway to stop the caravan".
The U.S. military has already begun delivering jersey barriers to the southern border in conjunction with the deployment plans.
Mexico's interior minister, Alfonso Navarrete, said on Sunday night the police were not equipped with any such weapon and had come under attack as immigrants threw rocks, bottles and firecrackers.
USA officials have told Reuters the support mission would be coordinated by the U.S. military's Northern Command.