The Pentagon will deploy up to 5,200 active duty troops to the U.S.-Mexico border in an effort to prevent members of a migrant caravan from illegally entering the country, a U.S. official said Monday.

About 2,100 National Guard troops already were fanned out across the border under an order from President Donald Trump earlier this year. In recent weeks, the president has been warning repeatedly about the dangers posed by a caravan of mostly Central American migrants, which has swelled to an estimated 7,000 people and is continuing its slow trek north through Mexico. Mexican govvernment officials have estimated about 3,600 migrants because at least 1,700 filed asylum applications in Mexico or accepted assistance to return to their home countries.

Administration officials said last week that they were considering a plan to send up to 1,000 active-duty troops to the border, but that deployment has increased to 5,200, according to the Department of Homeland Security official, who spoke on condition of anonymity because he was not authorized to publicly discuss the plans before a formal announcement Monday afternoon.

The troops are not expected to conduct law enforcement activities but instead provide support to Border Patrol agents manning the border. National Guard units have already been assisting by monitoring video surveillance feeds to direct Border Patrol agents manning the vast stretches between U.S. ports of entry.

The new deployment of active duty troops while likely include helicopter and other aviation units to help with transportation, according to a Defense official who was not authorized to speak about the deployments because they have not been finalized. The deployment could also include engineering units to build temporary housing, and headquarter units to coordinate activities, the official said.

"The orders are being drafted and some material is moving, construction-type material, 30 barriers, that sort of thing that they may need," Defense Secretary Jim Mattis said on Sunday. "We anticipate from what they thought they'll need."

Typically, migrant caravans travel in numbers to seek safety and avoid risks such as kidnap, rape and extortion. When the last migrant caravan reached the U.S. border in April, a majority of people presented themselves at ports of entry to request asylum, a legal way to enter the United States.

The Homeland Security official also said the president is expected to deliver a speech on Tuesday to outline further actions to halt the migrant caravan, which could include limiting, or halting, the ability of migrants to request asylum. That move would be predicated on national security arguments similar to those used to enact Trump's travel ban last year and would meet the same legal challenges by immigration advocacy and civil rights organizations.

White House spokesperson Sarah Sanders declined to detail other aspects of the new border security plan, and would not confirm whether Trump will deliver a speech on the topic this week.

"There are a lot of options that are being discussed right now," she said on Monday.

Trump on Monday again claimed, without evidence, that the migrant caravan may have “many gang members” and “some very bad people.” Reporters from USA Today and other media outlets, including The Associated Press, have not seen the presence of such individuals. Many of the migrants are families traveling with children.

"Please go back, you will not be admitted into the United States unless you go through the legal process," he tweeted. "This is an invasion of our Country and our Military is waiting for you."

The administration's latest moves are the latest in a series of efforts carried out to show a robust response to the migrant caravan as the midterm elections draw closer. Department of Homeland Security Secretary Kirstjen Nielsen on Friday showed off a recently-completed section of border fence in Calexico, Calif., that including a plaque proclaiming the "completion of the first section of President Trump’s border wall." That section had been deemed a priority and funded during the Obama administration.

On the same day, Customs and Border Protection Commissioner Kevin McAleenan toured ports of entry south of San Diego and explained how additional troops would help secure the border from any attempted rush by the migrants to rush the border. But McAleenan, who described the oncoming caravan as a "law enforcement situation," conceded that despite the added manpower, his agency has no way to speed up the process by which migrants can legally request asylum.

That's what happened when the last migrant caravan reached the U.S. border in April — 122 were caught trying to enter the country illegally, but 401 presented themselves at ports of entry to request asylum, according to data from U.S. Citizenship and Immigration Services.