A Mexican drug cartel scout and human smuggling guide was arrested this week when he was caught with six illegal immigrants on the Texas side of the U.S.-Mexico border, authorities said. 

Salvador De Jesus Romero Nunez, from Reynosa, Mexico, had guided the group across the Rio Grande when he was caught by Border Patrol agents and the Texas Department of Public Safety. Authorities had been tracking the group, who had just crossed the river into Texas. 

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They took six illegal immigrants into custody. Romero faces charges in Texas for human smuggling. Investigators later learned he works as a south and smuggling guide for the Cartel del Golfo, (Gulf Cartel), which is headquartered in Matamoros, Tamaulipas, Mexico, according to the Drug Enforcement Administration (DEA), which sits on the border across from Brownsville, Texas. 

Authorities at the border have seen Mexican cartel members operating in the area with more regularity in recent months. 

In June, a Gulf Cartel member was arrested upon being suspected of assisting five migrants cross illegally into the U.S. Earlier this month, two Mexican citizens with cartel ties were arrested coming across the Texas-Mexico border with rifles and armor-piercing rounds. 

"There is no greater public safety and national security threat than the Mexican drug cartels, who have exploited security vulnerabilities due to an unsecured international border," a Texas DPS spokesperson said at the time. 

Republicans have called for more action, including military action against cartels in Mexico itself — which has drawn rebuke from Mexican President Andres Manuel Lopez Obrador. 

Obrador has also criticized Texas Gov. Greg Abbott for establishing a floating barrier along the Rio Grande to prevent migrants from crossing.