This article by Richard Sisk originally appeared on Military.com, the premier resource for the military and veteran community.

President Donald Trump's effort to repel the "caravan" of migrants and political-asylum seekers from Central America heading north will be bolstered by more than 5,200 additional active-duty troops at the southern border, military and Customs officials said Monday.

Several hundred troops from Fort Knox and Fort Campbell in Kentucky are already on the move into southern Texas, said Air Force Gen. Terrence J. O'Shaughnessy, commander of U.S. Northern Command.

"By the end of the week, we will deploy over 5,200 soldiers to the southwestern border," he said.

O'Shaughnessy said the plan is to deploy the additional troops first to Texas and then to Arizona and California in support of U.S. Customs and Border Patrol.

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The troops will be armed -- "they are in fact deploying with weapons" -- but their mission will be to back up CBP in law enforcement, he said.

Should the plan be fully implemented, the additional 5,200 troops will join 2,000 National Guard members already in place, for a total of 7,200 on the border -- far exceeding the 2,000 U.S. troops in Syria and the 4,500 in Iraq.

The additional troops will augment the customs agency's own stepped-up efforts to secure the border, said CBP Commissioner Kevin McAleenan.

"You should return home and apply for the appropriate visa," he advised those in the caravan. "You will not be allowed to enter the U.S."

At a brief joint news conference with McAleenan at the Ronald Reagan Building in Washington, D.C., O'Shaughnessy did not state where all of the troops would be coming from -- apart from the mention of Forts Campbell and Knox -- but said the deployments were expected to last until at least mid-December.

He gave no estimate on the expected costs for the active-duty military of the mission that has been dubbed Operation Faithful Patriot. The National Guardtroops were sent to the border under a previous mission, Operation Guardian Support, which was strictly a support and surveillance role.

It was not immediately clear how the mission of the active duty-troops might differ from that of the National Guard. When the National Guard troops deployed to the border in April, the Pentagon stated that they would conduct "aviation, engineering, surveillance, communications, vehicle maintenance and logistical support."

Defense Secretary Jim Mattis told reporters traveling with him to Prague on Sunday that the rules of engagement for additional troops who might be sent to the border were still being worked out, according to media reports.

"The rules that the troops will be under -- I don't have that at this time," Mattis said.

O'Shaughnessy said the active duty troops would follow "posse comitatus" rules of federal law, which expressly bar members of the military from being used for law enforcement without the approval of Congress.

O'Shaughnessy said the additional troops would include units of the ArmyCorps of Engineers, which would assist in efforts to "harden" border crossing points with barriers.

He also said the troops would be bringing with them about 150 miles of concertina wire, which could be strung across points considered vulnerable.

"We're bringing in military police units. We're bringing in strategic airlift," O'Shaughnessy said.

He added that the deployed force would also include three combat engineering battalions and three medium-lift helicopter companies.

"As we sit right now, we have three C-130s and a C-17 that is ready to deploy with [Customs and Border Protection] personnel wherever they need to be" to stop illegal crossings, he said.

The initial caravan group, now believed to number about 3,500, was still several hundred miles away from the border and was expected to shrink. McAleenan said many would likely take up Mexico's offer of shelter and asylum.

However, McAleenan said a second group of several thousand migrants was forming at the Guatemalan border with Mexico and were intent on joining the initial caravan.

"We've got to be prepared for the potential arrival of a very large group," McAleenan said.

Trump has made the progress of the caravan and the threat that thousands of migrants would come "pouring over the border" a constant theme at his rallies leading up to the Nov. 6 midterm elections.

Hours before the latest troop deployments were announced, Trump sent out a tweet: "Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border. Please go back, you will not be admitted into the United States unless you go through the legal process. This is an invasion of our Country and our Military is waiting for you!"

Last week, in an interview with ABC News, Vice President Mike Pence did not respond directly when asked whether Trump was considering a complete shutdown of the southern border.

"What we need to do is secure our border," Pence said. "The president will take steps to do that. But we also need to reform our laws."

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