FIRST ON FOX: Border Patrol agents patrolling the Rio Grande Valley Sector were fired upon from across the Mexican border on Wednesday, multiple law enforcement sources told Fox News. 

The Special Operations Group, part of Border Patrol Tactical Operations (BORTAC), were shot at from beyond the border, and then returned fire – nobody on either side was hit.

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In a statement to Fox News, Customs and Border Protection (CBP) confirmed that agents responded to a report of suspected migrants near Fronton. The statement also confirmed that the incident is being reviewed by both the FBI and CBP’s Office of Professional Responsibility.

Fox is told that the Mexican military had engaged with cartel members in a shootout on the Mexican side, at which point a man fled and tried to cross into the U.S. via a nearby river. When a BORTAC agent jumped into the water to rescue him, the agent was fired upon.

It occurred in the same area where Texas National Guard members were shot at from Mexico just last month. The suspected shooters were believed to be gunmen from a drug cartel, but it was not clear. No National Guard members were hurt.

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It is also where Fox News personally witnessed tracer fire from a cartel machine gun coming into U.S. territory.

That area in Roma is viewed as cartel land and is where the Gulf cartel and Cartel Del Noreste fight for control of the city in Mexico across from Roma – Ciudad Miguel Aleman.

Heavily armed groups are becoming a more common sight along the Texas-Mexico border, authorities said. Last month, Texas Department of Public Safety officials told Fox News that suspected cartel members involved in human smuggling were wearing tactical gear and armed with AK-47s while taunting National Guard soldiers across the Rio Grande. 

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Mexican cartels have been known to commit acts of violence on migrants traveling to the U.S.-Mexico border, but it is rare for them to confront American law enforcement or military troops. 

There were more than 178.840 migrant encounters in December, and Republican lawmakers have warned that the continuing crisis at the southern border is only serving to encourage cartels and criminal organizations that facilitate much of the human smuggling, trafficking and the drug trade at the border.