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.

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.