Soldiers from Fort Bragg, Joint Base Lewis-McChord, Fort Stewart, Fort Campbell, Fort Knox, Fort Riley among other bases will be sent to the border, Fox News Pentagon reporter Lucas Tomlinson said.
"The units that are normally assigned weapons, they are in fact, deploying with weapons," General Terrence J. O'Shaughnessy told the media on Monday.
The mission is called "Operation Faithful Patriot," and is headed by Army Lt. Gen. Jeffrey S. Buchanan, who operated in Puerto Rico in 2017 following the devastating Hurricane Maria.
The troops will begin their deployments starting Tuesday.
The US Air Force is also reportedly prepared to airlift an additional 400 Border Patrol agents to the southern border.
Earlier on Monday, the caravan crossed from Guatemala into Mexico via the Suchiate River, which is near Mexico's southernmost point, videos posted on social media show.
Hours prior, President Donald Trump tweeted that there are "Gang Members and some very bad people" in the caravan. "This is an invasion of our Country and our Military is waiting for you!" he said.
Isabel Garcia, co-founder of Coalición de Derechos Humanos, told Radio Sputnik on Thursday that the troop deployment is a "violation of the Posse Comitatus Act." The law, passed in 1878, forbids the military from deploying for the purpose of law enforcement except when authorized by Congress, Sputnik News reported.
"We've actually gone to Congress in decades past, where the military has agreed with us that they have no place along the border because they are trained to kill," Garcia said.
According to an anonymous official who spoke to Fox News, the troops will be present in order to offer "logistical support" to the National Guard at the border.