U.S. Customs and Border Protection officers have apprehended an additional 1,600 people attempting to illegally enter the country from Mexico since April 15 as a result of the deployment of National Guard troops to the southwest border, CBP and defense officials said Wednesday.

National Guard officials overseeing the border state deployments said troops helping monitor the international boundary have freed up more border agents to physically guard the border. The result has led to a surge in the amount of criminal activity agents have stopped.

[Related: Illegal immigrant apprehensions at US-Mexico border hit highest levels since Trump took office]

The increased surveillance and communication between guardsmen and border officers also led to CBP intercepting an additional 451 people who were turned back before illegally entering the U.S.

Those numbers could tick up considerably if the 4,000 National Guard troops President Trump approved on April 4 are called on in a future request from CBP.

As of Wednesday, 775 troops have been deployed and are on the ground providing "direct support on the ground" in seven sectors assisting law enforcement officers.

Troops are providing support from the air, surveillance back-up, and assistance with infrastructure projects like vegetation clearing and road maintenance, not including to the border wall construction. Another task is to specifically free up agents to leave their desks and get back out to the field. The troops monitoring remote video surveillance systems have then been able to report sightings to a greater field of agents and thus, the number of apprehensions has increased, officials said.

"Those folks are giving us the additional situational awareness in the radio rooms ... which are allowing the Border Patrol agents sitting in those areas to go into the field," said one National Guard official, who described the addition of the Guard as a "force-multiplier" for the CBP.

"As a reminder, these guardsmen are not carrying out law enforcement duties," an official representing the Texas National Guard said.

Guardsmen have been deployed to the following Border Patrol sectors: 200 to the Rio Grande Valley, 120 to Laredo, 90 to Del Rio, 70 to Big Bend, 110 to El Paso, 135 to Tuscon, and 50 to Yuma.

In late April, the California National Guard said 200 guardsmen were in training at Camp Roberts and would be deployed in early May. Around 55 troops are already working in those sectors.

The deployment is funded through the end of fiscal year 2018, September 30. Ronald Vitiello, CBP deputy commissioner, said in April the intent of the mission is for CBP to regain operational control of the border.

[Also read: Customs and Border Protection sees 'great uplift' in employee morale under Trump]

A National Guard spokesman on Wednesday said raising interdiction rates is the first step to Vitiello's goal.