The officers were traveling in six patrol pickups and searching for the bodies of seven men and three women whose heads had been dumped outside the town’s slaughterhouse earlier Sunday, Mr. Martínez said.

The heads were left with a message threatening the drug cartel La Familia, whose home base is in neighboring Michoacan State.

Teloloapan is near an area shared by Guerrero and Michoacan that is known as Tierra Caliente for its steamy weather. Drug traffickers have used the violent, mountainous zone for years to grow marijuana and opium poppies.

The region has been plagued by drug violence in recent years as drug gangs have fought to control it. The authorities say the fighting has severely battered La Familia.

Soldiers have been sent to the area, but that has not stopped gunmen from killing priests, politicians, police chiefs or anyone else who gets in the way.

In September 2010, nine police officers were kidnapped in Teloloapan as they were investigating the death of a man in the village of El Revelado. The bodies of eight of the officers were found days later. Six had been dismembered. One officer was found alive.

More than 47,000 people have died in drug violence nationwide since President Felipe Calderón began a crackdown on drug cartels in December 2006.