MONTERREY, Mexico — Mexico's army dug up human remains in 11 pits at an abandoned ranch in the northern Mexican state of Nuevo Leon, a state prosecutor's official said on Saturday.

Authorities believe the graves contain at least 11 bodies, the official said, who spoke on condition of anonymity because he was not authorized to talk on the record.

State police investigating the site along with the army said there might be dozens of bodies buried at the ranch, but because only small bones were found it was difficult to determine the number, the official said.

The mass grave was discovered Friday by soldiers patrolling in the municipality of Juarez, about an hour's drive from the wealthy state capital of Monterrey. This is the fourth time remains have been uncovered in Juarez this year.

Authorities also found in separate rooms at the site mattresses riddled with bullets, spent AK-47 cartridges, large metal barrels and empty containers with gasoline traces, the official said. This led police to believe the bodies were burned in the barrels before being buried, he said.

Near the graves, soldiers found metallic rods nailed to trees that may have been used to tie victims' hands so they could be tortured, the official said.

Nuevo Leon has been a scene of constant killings and reprisals among rival drug traffickers since a rupture between the Gulf and Zeta cartels in late 2009.

Mass graves sometimes containing hundreds of corpses have been found across the U.S.-Mexico border region, where cartels are engaged in bloody turf battles. More than 400 bodies were found in a series of clandestine graves in Tamaulipas and Durango states since April.

Mexico's Defense Department said Friday that it was sending close to 3,000 soldiers to Tamaulipas to aid the embattled northern state in weeding out corrupt police and recruiting and training new ones.

Elsewhere Saturday, Guerrero state police said five people were killed in the Pacific resort city of Acapulco, two of them in the tourism district. The bullet-pierced bodies of a taxi driver and a 14-year-old Guatemalan boy were found in a house near the main hotel boulevard, the Guerrero Public Security and Civil Protection Secretariat said.

A 16-year-old boy was discovered with gunshot wounds to the head in an Acapulco fish market. Two other men were found dead in another neighborhood.

Five other slain people were found in other parts of Guerrero state, including a 16-year-old boy in the municipality of Cuajinicuilapa who suffered a blow to his head.

In the Pacific Coast state of Jalisco, more than 40 masked men burst into a cantina Saturday morning and opened fire, killing four people, the state prosecutor's office said. The gunshots mingled with fireworks from a nearby religious ceremony, the office said

Authorities in Jalisco and nearby Michoacan state are working together to look for the attackers.

In the Gulf coast state of Veracruz, federal police said they arrested the leader of the Zeta cartel's operations in the state.

The suspect, whose name is either Alberto Gonzalez Pena or Franco Buena Pena, was in charge of transporting drugs to northern and central regions of the country, the Public Security Secretariat charged. He is also linked to the kidnapping of a municipal government worker in 2007 and two abductions in 2010, the statement said.

Associated Press writers Gustavo Ruiz in Morelia and Sergio Flores in Acapulco contributed to this report.