Two Southern California men pleaded guilty Tuesday to smuggling 28 pounds of heroin into the United States using drones.

"This is believed to be the first international narcotics seizure by US law enforcement involving the use of drones by Mexican drug traffickers," according to a statement issued by federal prosecutors.

Court documents showed that the scheme involved two men, Jonathan Elias and Brayan Valle, both of El Centro, California. Elias was apparently paid $100 to go pick up Valle in nearby Calexico, a border town.

"According to their guilty pleas, on or about April 28, 2015, Elias drove Valle to pick up packages of drugs that were smuggled by drones near an agricultural field in Calexico near the border," the statement said. "Using a drone controller, Valle picked up packages of narcotics and placed them inside a bag. They placed the bag in the trunk of their vehicle and were subsequently stopped by US Border Patrol agents. As part of their plea, defendants admitted that they knew that there were narcotics inside the bag, but did not know the quantity or type of narcotics inside the bag."

"With border security tight, drug traffickers have thought of every conceivable method to move their drugs over, under and through the border," United States Attorney Laura Duffy said in the same statement. "We have found their tunnels, their Cessnas, their jet skis, their pangas, and now we have found their drones."

Neither prosecutors nor the defendants’ attorneys immediately responded to Ars’ request for comment.

In January 2015, police in the northern Mexican city of Tijuana found a drone "loaded" with drugs that crashed in a supermarket parking lot near the US-Mexico border.