The boxes containing the heads were dumped by a roadside
Five severed heads have been found inside ice coolers by the side of a road in Mexico, police say.
A police patrol made the grim find in the central state of Jalisco, on a road leading to the city of Guadalajara.
The heads were found with messages addressed to rivals of the killers, who were assumed to be involved in Mexico's bitter and violent drug war.
Jalisco is close to Sinaloa state, scene of many high-profile killings and home to the powerful Sinaloa cartel.
The state is home to a number of key figures in the drug trade, including Mexico's most-wanted man, Joaquin "Shorty" Guzman.
Mexico is currently in the midst of a battle between feuding drugs cartels.
The gangs are fighting a vicious turf war in the north of the country over lucrative smuggling routes into the US.
Police in Jalisco said the heads found on Tuesday were severed before being packed in ice and dumped by the roadside.
"They were recently severed heads, cut off about four hours before they were found," a spokesman said.
They were accompanied by a note thought to be from the killers threatening rival gangs.
Drug wars in Mexico have claimed thousands of lives in recent years, with more than 1,000 people killed already in 2009.
Some 186 people were decapitated during 2008 out of a total of 5,600 killed in total, Mexico's Human Rights Commission says.
In an effort to dampen the rising tide of murders, Mexico's president last week deployed thousands of troops to Ciudad Juarez, near the US border, to try to wrest control of the city from the gangs.