The mutilated corpses and dismembered body parts of 12 people were dumped in seven locations across the metropolitan area of the Mexican city of Monterrey on Tuesday in a spate of violence that unnerved residents of Mexico's industrial capital.

The gruesome discoveries recalled a bloody period in the 2010s when cartel conflicts engulfed the city and bodies were left in the streets or hanging from bridges.

Such brutality had largely subsided in Monterrey, which was recently chosen to be the home of a new Tesla (TSLA.O) car plant.

Authorities said Tuesday's events appeared to be a coordinated attack and were likely sparked by an internal conflict within a criminal group based in the bordering state of Tamaulipas.

"From the messages that were left (near the bodies), there's a correlation," said Pedro Jardon, the attorney general of Nuevo Leon, in response to questions from reporters on Tuesday afternoon.

Photos of the supposed messages circulating in the local press and on social media suggested the murders were carried out by the Northeast Cartel and were retribution for the alleged infiltration of the group.

The attorney general's office did not confirm the authenticity of the photos.