He's expressed outrage about the group of several thousand migrants, which is slowly making its way north from Mexico's border with Guatemala, and said in a tweet on Monday that the caravan included "unknown Middle Easterners".
About 2,100 National Guardsmen are already deployed to the border, following a presidential order in April.
Defense Secretary James Mattis could sign the deployment orders as soon as today.
The official said roughly 800 soldiers will be sent to the area to offer "logistical support", including providing tents and vehicles.
Trump's deployment of the military along the border would also face restrictions that make it more hard to deport illegal aliens.
"I am bringing out the military for this National Emergency".
"I need surgery, I want to do in the United States because in my country nobody helps me", says Sergio Caceres, 40 years old, in a wheel chair that grows a friend met in the caravan.
Pentagon spokesman Navy Captain Bill Speaks said the Defense Department was now working with the Department of Homeland Security "to determine the specifics of our support" to border authorities.
Thousands of Honduran migrants gathered in a Guatemalan city near the border with Honduras Tuesday to prepare for a new caravan that would follow in the footsteps of a larger group now marching to the U.S. -Mexico border, posing a fresh challenge to Guatemalan and Mexican authorities seeking to contain a surge in mass migration.
The issue has become a rallying cry for the USA president, who has taken a hard line on illegal immigration and has repeatedly kept the story in the headlines in the run up to America's midterm congressional elections that could see the Democrats regain some degree of power.
Some of them, including women and children, have said they're fleeing because of widespread violence and poverty.More news: NBC cancels Megyn Kelly's morning show
Caravan members also face the threat of being robbed, kidnapped or killed by Mexican gangs that extort migrants on their journey.
Dr Amanda Klekowski von Koppenfels, an expert on migration at the University of Kent's Brussels School of International Studies, said Trump will to use the issue to secure votes in midterm elections early voting.
Many in the caravan may not qualify for asylum even if they reach the border, as the USA does not consider escapes from poverty and certain types of violence as qualifying factors.
"The United States also has a message for those who are now part of this caravan or any caravan which follows: You will not be successful at getting into the United States illegally no matter what", Pompeo said at a briefing with reporters at the State Department.
The Pentagon will send "several hundred" troops to the United States-Mexico border, a US official said Thursday, after President Donald Trump said the military would be used to tackle a "national emergency" on the border.
Early Thursday, they set off from the town of Mapastepec in the southern Mexican state of Chiapas, moving on to the next stop in their long march north.
Some rode on trucks but most made the trek to the town of Pijijiapan on foot.
She left her two children back in Honduras and plans to get a job in the U.S.to send money back home so that her younger siblings and her children can afford to go to school.
As many as 5,000 migrants were reported to have massed in the Mexican city of Tapachula by Sunday evening, some 3,800 kilometers (2,400 miles) from the USA border.
The UN estimates that about 7,000 people are part of the caravan, which departed on 13 October with Honduras.