The top USA general overseeing a deployment of more than 5,200 troops to the border with Mexico said on Tuesday that troop levels would rise further but declined to say how high or estimate what the operation will cost.
United States officials last week said about 800 active-duty troops would be sent to provide assistance - mainly in the form of logistical support - to border guards working along the frontier.
In an interview Monday, Trump said the USA would build "tent cities" for thousands of Central American migrants making their way through Mexico to the United States.
The announcement comes as President Donald Trump has been trying to focus on the caravan just a week before the midterm elections. More than 1,500 of the original group have applied for asylum in Mexico.
Air Force General Terrence O'Shaughnessy, head of the U.S. military's Northern Command, told reporters the 5,200 troops would focus on trying to "harden" border crossings and surrounding areas, with work done by combat engineering battalions with experience building temporary fencing.
"Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border", Trump wrote without providing evidence, doubling down on the hardline anti-immigrant rhetoric that helped fuel his 2016 election victory.
But Mexican officials seem intent only on seeing the caravan melt away as it travels toward the USA border.
In private, Homeland Security officials acknowledge they were alarmed by scenes of migrants breaking through a gate at Guatemala's border with Mexico last week.
"We go for about a month, I stopped counting the days, we are helped by Almighty God and the good people you meet on the way", says this mother of a family.
"If they apply for asylum, we are going to hold them until such time as their trial takes place".
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The Pentagon claimed that directs to the border with Mexico more than five thousand troops.
In April, Trump ordered up to 4,000 National Guardsmen to head to the border as a different migrant caravan wound its way north.
The White House is also weighing additional border security measures, including blocking those traveling in the caravan from seeking legal asylum and preventing them from entering the U.S.
The troops are expected to perform a wide variety of functions such as transporting supplies for the Border Patrol, but not engage directly with migrants seeking to cross the border, officials said.
The troops will include military police, combat engineers and others helping on the southern border.
The Pentagon last week approved a request for additional troops at the southern border.
He added: "This is an invasion of our Country and our Military is waiting for you!"
Perhaps Trump doesn't understand that it is legal for anyone on US soil, even if they arrived without documentation or authorization, to claim asylum and start a legal process that can end with them being allowed to stay.
Migrants are entitled under both USA and worldwide law to apply for asylum.
The projected US deployment is already roughly the same size as the USA military contingent in Iraq.