Armed men later ambushed a federal police patrol, killing five officers and wounding seven in the hotspot of drug violence.

State prosecutors said in a statement that six bodies and severed heads were discovered at the entrance to the Michoacan town of Acahuato. The victims had not been identified.

Later, state Public Safety Secretary Minerva Bautista said a group of at least a dozen armed men attacked a federal police convoy, opening fire on the vehicles from a highway overpass near the city of Maravatio. Two of the wounded officers were reported in serious condition.

Michoacan is the cradle of La Familia cartel, which authorities blame for a string of recent beheadings and the killings of police and soldiers.

Also on Friday, four severely beaten men were seen walking along a busy street in the Michoacan town of Zamora carrying messages signed by La Familia.

"Society, don't judge us. We're cleaning your city," read one note.

Last week, four men who had been beaten and tortured marched near Zamora's train station carrying similar signs and yelling that they were rapists and thieves.

President Felipe Calderon first launched his crackdown against drug cartels in Michoacan, sending thousands of federal police and soldiers to his home state after taking office in late 2006.

Drug violence has killed more than 15,000 people throughout Mexico since then.