U.S. Border Patrol agents came under fire while working on the southern border from gunmen operating inside Mexico, according to various officials.

U.S. Customs and Border Protection (CBP) confirmed to Fox News that shots were fired from the Mexican side of the El Paso, Texas sector on Wednesday afternoon. The CBP said that agents were involved in a “use of force incident while responding to reports of shots fired near the border in the Ysleta Station area of responsibility in Texas.” Sources confirmed that CBP agents returned fire.

The FBI later confirmed the shooting in a statement to Fox News, saying it happened “by the Ysleta USBP Station – Lopez Gate” and that their agents are investigating it as an “assault on federal agents.”

“FBI El Paso was notified of the May 8th shooting that occurred by the Ysleta USBP Station – Lopez Gate. The FBI El Paso Violent Crime Task Force and the FBI Evidence Recovery Team were deployed to collect evidence at the crime scene.,” the FBI said. “The FBI El Paso’s Violent Crime Task Force is working closely with the U.S. Custom and Border Protection’s Office of Professional Responsibility on this assault on a federal officer investigation. As this is an ongoing investigation, no further details may be given at this time.”

CBP said that no agents were injured during the incident and that an investigation is underway.

“There are no reported injuries at this time,” the CBP said in a statement. “The incident is under review by Customs and Border Protection’s Office of Professional Responsibility.”

The shocking incident is not the first time agents have come under fire during a patrol.

The CBP said that this was the second incident in recent weeks.