The bullet-ridden bodies of the cartel members were discovered in the north-central state of Zacatecas. Earlier this week, two missing police officers were found hanging from a bridge in the same area.
Eighteen bodies were discovered Friday after what appeared to be a shootout between members of rival drug gangs in northern Mexico.
State security department spokeswoman Rocio Aguilar said there was evidence the shootout resulted from a confrontation between gunmen from the Sinaloa and Jalisco criminal cartels over drug trafficking routes.
Three vehicles, one of them burned out, were also found at the scene.
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Local media reported several similar shootouts this week in the same area.
On Wednesday, seven people were also shot to death in a neighboring city in the state.
On the same day, the bodies of two abducted police officers were found hanging from a bridge in the state capital.
Gunmen from cartels often hang bodies to send out a message to either authorities or rival members, but they seldom target law enforcement officials.
Aguilar said authorities have not found a link between the discovery of the officers' bodies and the latest gun battle.
What triggered the shootout?
The state of Zacatecas, once dominated by the old Zetas cartel, has been the scene of many inter-cartel battles.
The township of Valparaiso, where the shooting occurred, borders Jalisco state, a stronghold of a powerful cartel called Jalisco Nueva Generacion (Jalisco New Generation).