Suspected drug gangs have dumped the severed heads of six police officers outside a church in the northern Mexican state of Durango, police said, BBC reported.
They said the beheadings were a revenge attack by the Gulf cartel for the killing of 10 gang members last week.
More than 14,000 people have died in drugs-related violence since 2006, some 60 in the past three days alone.
President Felipe Calderon has deployed thousands of troops across the country in an effort to crush the cartels.
The severed heads were left in plastic bags near the church in Durango state before dawn.
They were discovered by garbage collectors, the state attorney general's office said.
On Tuesday, gang members killed at least 12 people in Tijuana, across from San Diego, decapitating four of the victims - a hallmark of Mexico's brutal drug gang violence.
The Obama administration delivered five helicopters to Mexico on Wednesday to help it in its fight against drug cartels, which are battling for control over lucrative smuggling routes into the US.
Washington says the rising death toll is a sign the drug gangs are weakening under President Calderon's military crackdown, which has seen some 49,000 extra troops deploy across Mexico.
But Mexicans are angry at the army's inability to stop the violence and have called for a withdrawal in some cities, Reuters news agency reports.