At least 14 bodies have been discovered in a series of mass graves in Nuevo Leon, north Mexico.

State authorities said they had found three whole corpses, along with other human remains stored in 18 separate bags. They were buried in a vacant lot in the municipality of Benito Juarez, 20 km east of state capital Monterrey.

The spokesman for the attorney general said that the exact number of bodies had not yet been determined, as authorities had to “piece together” the body parts.

The site was found by civilians walking around the area. The corpses were reportedly in an advanced state of decomposition.

The discovery would be the second largest mass grave found in the state, after 51 bodies were found in July. There have been no arrests in either case.

Monterrey, long seen as one of Mexico’s most peaceful cities, has become a battleground between the Gulf Cartel and the Zetas, who are struggling for control.