The Zetas cartel's boss in Ciudad Victoria, the capital of the northeastern Mexican state of Tamaulipas, died in a shootout with army troops, the Defense Secretariat said.
Carlos Alberto Fernandez Hernandez and three associates were killed last Friday, the secretariat said in a statement.
"Mexican army personnel providing public safety support in Tamaulipas were the target of an armed attack by members of an organized crime group" while on a reconnaissance mission in Ciudad Victoria, the secretariat said.
Soldiers responded to the attack "to defend themselves and citizens," engaging in a shootout "in which four attackers died," the secretariat said.
Fernandez had been identified as a personal assistant of Los Zetas leader Heriberto Lazcano Lazcano, coordinating the acquisition of houses, obtaining vehicles and recruiting people for the cartel boss, the secretariat said.
Fernandez had been running the cartel's operations in Ciudad Victoria for just four months, smuggling drugs, staging kidnappings, stealing fuel and running extortion rackets, the Defense Secretariat said.
He was also allegedly involved with Gregorio Villanueva Salas, known as "The Czar of Piracy," in the bombings that targeted media outlets, schools and businesses in Matamoros, a border city in Tamaulipas, in May and June.
Villanueva was arrested by army troops on June 14 in Monterrey, the capital of the northern state of Nuevo Leon, along with three other members of the gang.
Soldiers seized two rifles, two handguns, 811 rounds of ammunition, 35 ammunition clips, a vehicle, 38,000 pesos (about $2,883), $29,000, tactical equipment and communications gear after the shootout.
Lazcano Lazcano deserted from the Mexican army in 1999 and formed Los Zetas with three other soldiers, all members of an elite special operations unit, becoming the armed wing of the Gulf drug cartel.
After several years on the payroll of the Gulf cartel, Los Zetas, considered Mexico's most violent criminal organization, went into the drug business on their own account and now control several lucrative territories.
Tamaulipas and neighboring Nuevo Leon state have been rocked by a wave of violence unleashed by drug traffickers battling for control of smuggling routes into the United States.
The army is carrying out "Operation Northeast" in Tamaulipas, Nuevo Leon, Coahuila and San Luis Potosi states in an effort to weaken the drug cartels that operate in the region. EFE