(CNN)National Guard troops stationed along the US-Mexico border have contributed to 1,600 apprehensions of people crossing the border illegally and the capture of about 1,000 pounds of marijuana in their three-and-a-half weeks on the job, according to a Customs and Border Protection official.
National Guard troops involved in 1,600 apprehensions at Mexican border
The official said the National Guard troops have also contributed to 451 "turn backs," where individuals abandon an attempt to illegally cross into the US.
The official did not have comparison numbers available, so it was not possible to determine if those figures were substantially more than if National Guard troops had not been dispatched to the border.
There were roughly 38,000 apprehensions of people trying to cross the border illegally each of the past two months, according to data from the Department of Homeland Security. That's roughly 2.5 apprehensions per agent stationed at the border, though not all are in the field. Monthly apprehensions fluctuate with the season and other trends, and it is difficult to attribute changes to any one cause.
The official described the troops as a "force multiplier" and said they are are relieving Border Patrol agents from a variety of responsibilities that are not on the front lines, such as monitoring surveillance systems from control centers. That allows CBP to place additional agents on the ground where they can make arrests.
At a separate event on Tuesday, Defense Secretary James Mattis said National Guard forces are not performing arrests.
"Right now we are not having any contact with migrants," he said.
Homeland Security Secretary Kirstjen Nielsen "has not asked for that support and I have no plans to provide that support for any contact between the National Guard and migrants," Mattis added.
A National Guard official said the troops do face a restriction: Those monitoring surveillance equipment, such as cameras, are prohibited from viewing the Mexico side of the border.
Those troops are "currently looking in the continental United States, not across the border," the National Guard official said. "We are not looking deep into Mexico for what would be considered more of an intelligence collecting capacity."
The official added National Guard troops stationed in observation lookouts along the Texas-Mexico border are operating under a different legal authority and are not barred from inspecting Mexican territory with their binoculars.
Approximately 775 National Guard troops are currently working in the border region in response to President Donald Trump's April directive.
A CBP official said the agency is working on a third request for assistance from the Department of Defense. That request has several additional steps before it is sent to the Defense Department.
The CBP and National Guard officials spoke on a conference call with reporters on the condition that they not be identified by name.