In the Mexican city of Monterrey mutilated and dismembered body parts of 12 people have been found in seven locations, including some of the wealthiest neighborhoods in the country, on Tuesday. 

The head of security official of Nuevo Leon state, Gerardo Palacios, has said that the killings appear to be related to an internal dispute between a drug cartel which is based in the state of Tamaulipas.

“From the messages that were left (near the bodies), there’s a correlation,” Pedro Jardon, the attorney general of Nuevo Leon, told reporters on Tuesday afternoon.

A Reuters report said that the images of the supposed messages left around the bodies circulating online and in the press suggested that the killings were done by the Northeast Cartel and were retribution for alleged infiltration of the group. However, the authenticity of the photos was not confirmed by the attorney general’s office.

Drug cartels in Mexico often leave dismembered bodies on streets, often with banners threatening officials or rival gangs.

The grisly discovery came the day after drug cartel banners had been left around the city. It contrasted with Monterrey’s recent reputation for success after it was chosen as the site of a new Tesla car plant.

Monterrey suffered waves of drug cartel violence in the 2010s, but had become more peaceful until Tuesday’s events.

(With agency inputs)