Nine people were killed, including four women, when gunmen stormed a bar and opened fire in Mexico’s violence-torn state of Guanajuato, authorities said Thursday.

It was at least the third such bar massacre in as many months in Guanajuato, where a local gang is waging a war with the Jalisco cartel. The common denominator in the attacks is that the attackers simply tried to kill everyone in the bars, including the waiters. In Wednesday night’s attack in the town of Apaseo el Alto, the attackers left handwritten posters on the bar’s blood-stained floor. The messages were signed by the Santa Rosa de Lima gang, whose now-imprisoned leader is known as “Marro” or Sledgehammer.

The messages appeared to accuse the bar owners of supporting the rival Jalisco cartel.

Photos from the scene showed the bodies of several waitresses in miniskirts lying in pools of blood at the bar. The municipal government of Apaseo el Alto said two other women were injured in the attack, but their health condition is stable. In October, twelve people, six of them women, were killed in an attack on a bar in another city of Guanajuato. A similar bar attack in another city left 10 dead in September. Guanajuato-based security analyst David Saucedo said the attacks targeted specific bars — whose owners may have refused protection money or sold drugs from rival gangs — but were indiscriminate when targeting. “Some of the attacks were carried out to kill drug dealers, guards or cartel members who were out at bars,” Saucedo said. “But there are massacres because they kill both waitresses and customers.” There are signs that the conflict in Guanajuato, Mexico’s most violent state, has turned into a proxy battle between Mexico’s two most powerful drug cartels. The Sinaloa cartel now appears to be supporting the Santa Rosa de Lima gang in its fight against Jalisco.