The Mexican government has confirmed that the Gulf Cartel's top leader was killed during a day's worth of violence south of the border in Matamoros.
Mexico's federal government reported through its official Twitter account that Cardenas-Guillen was killed during a battle with Mexican Navy marines.
The El Milenio newspaper is reporting that Gulf Cartel leader Antonio Ezequiel Cardenas-Guillen was killed in Matamoros.
A spokesman with the Mexican Navy told El Milenio that Cardenas-Guillen and three of his gunmen were killed in a battle with Marines.
The identity of the other men who were killed was not immediately available.
No further details were available but residents of Matamoros have used Twitter to report several hours of grenade explosions and heavy gunfire throughout the city.
Cardenas-Guillen went by the nickname "Tony Tormenta" and reportedly took over the Gulf Cartel following the arrest of his brother Osiel Cardenas-Guillen.
The U.S. Department of Justice had been offering a multi-million dollar reward for the capture of Cardenas-Guillen.
The reward remains in place for other leaders of the Gulf Cartel and their former allies Los Zetas.
The Brownsville Herald reported that 47 people were killed in the daylong violence in Matamoros on Friday.
Mexican authorities temporarily closed the northbound lanes of the three international bridges between Matamoros and Brownsville.
All three bridges are now open.
University of Texas at Brownsville officials cancelled Friday evening classes and closed the campus throughout the weeken in light of the violence.
Action 4 News will post more information as it becomes available.