Mexico ? At least 30 gunmen burst into a drug rehabilitation center in a Mexican border state capital and opened fire, killing 19 men and wounding four people, police said. Gunmen also killed 16 people in another drug-plagued northern city.

The killings marked one of the bloodiest weeks ever in Mexico and came just weeks after authorities discovered 55 bodies in an abandoned silver mine, presumably victims of the country’s drug violence.

The bullet-riddled bodies of 14 men and two women were found Friday in different parts of Ciudad Madero, a city in the northeastern state of Tamaulipas, where violence has surged this year amid a turf battle between the Gulf cartel and its former ally, the Zetas gang of hit men.

Police had no information on suspects.