Nine decapitated and dismembered bodies were found in an abandoned van in the southern Mexican state of Guerrero, authorities said on Friday.
The bodies were all men and were found late Thursday opposite a hospital in the town of Tlapehuala. They had been packed in 18 black plastic bags, the public security ministry said in a statement issued in Mexico City.
"Nine bags contained the heads and parts of the bodies and nine bags the torsos," the statement said.
Seven of the victims had been shot in the head.
Two threatening messages signed in the name of the Familia Michoacana drug cartel had also been left there.
Violence has increased in recent days in the state of Guerrero, on Mexico's Pacific coast that is home to the world-famous resort of Acapulco.
More than 5,500 people have been killed so far this year in Mexico in incidents linked to organised crime.