MEXICO CITY (AP) — Mexican army soldiers said Friday they came under fire from drug cartel gunmen in the northern border city of Nuevo Laredo, across from Laredo, Texas, and returned fire, killing 12 gunmen.

The Defense Department said three army patrol trucks were hit by gunfire, but no troops were hurt.

The gunmen are believed to belong to the Cartel of the Northeast, a split-off of the old Zetas cartel.

The department said one of the attackers’ burned-out pickups was left at the scene, and eight assault rifles and two .50-caliber sniper rifles were also found. Nuevo Laredo has been the scene of bloody gunfights in recent years.

On April 1, the U.S. consulate in Nuevo Laredo issued an alert citing “reports of multiple gunfights and blockades throughout the city of Nuevo Laredo. U.S. government personnel are advised to shelter in place.”

On Jan. 4, the consulate wrote that “organized crime activity (including gun battles, murder, armed robbery, carjacking, kidnapping, forced disappearances, extortion, and sexual assault) is common” in Nuevo Laredo. “Heavily armed members of criminal groups often patrol areas in marked and unmarked vehicles and operate with impunity. Local law enforcement has limited capability to respond to crime incidents.”

Also on Friday, armed men killed five state police officers and wounded two others in the central state of Guanajuato, where 26 recovering addicts at a drug rehabilitation center were massacred earlier this week.

Gov. Diego Sinhue Rodriguez wrote in his Twitter account: “I regret what happened to the five officers … we will be intensifying our efforts to equip and train security personnel.”

Guanajuato has been the scene of bloody turf battles between the Jalisco drug cartel and the local Santa Rose de Lima gang. The killings have made it Mexico’s most violent state.