Mexican police are investigating the killing of three men who were found with notes pinned to their bodies carrying threats to local authorities.
Investigators in the northern state of Nuevo Leon believe two victims found there were killed by drug cartels.
Two more bodies were also found in the state of Quintana Roo - one of them carried a note.
President Felipe Calderon has been sending thousands of troops to several Mexican regions to tackle drug cartels.
In Nuevo Leon, Governor Natividad Gonzalez said security measures for local officials would be stepped up.
More than 30 people have died this year in the state in violence believed to be drug-related.
At least seven deaths in Quintana Roo have been linked to drug cartels.
The latest victims were found on the outskirts of Cancun - their hands and feet were tied and their heads covered with tape.
Unconfirmed reports say that one of the bodies had a note pinned to it which said: "Drugs are better for all, grass."
Last year, more than 2,000 people died in cartel-related violence - some of the victims were tortured or beheaded.