More than a dozen bodies were unearthed in a troubled region of southwestern Mexico where the military also engaged in a deadly firefight that killed one person, AFP reports according to the authorities.
In Michoacan state, which has been rocked by violence involving drug cartels and vigilantes, naval staff members were involved in a shootout with suspects in the town of Sahuayo, leaving one person dead, a prosecutor's office source said.
Meanwhile three people were found dead in Morelia, the state capital, and in neighboring Guerrero state authorities said they had now discovered 21 bodies in two mass graves. On Monday they said they had dug up 12 bodies in two villages near Taxco, a colonial city known for its silver.
Authorities have regularly found bodies in mass graves across Mexico in recent years, often linked to drug cartel wars or violence against migrants on their way to the United States.
Fed up with local police failure to curb the Knights Templar cartel's reign of violence and extortion, civilians began to form vigilante units a year ago in Michoacan state's Tierra Caliente farming area.
The movement has since grown, posing the biggest security challenge of President Enrique Pena Nieto's administration.
Pena Nieto deployed thousands of troops to Michoacan in May, but the continuing violence forced him to focus more forces last month in Tierra Caliente.
In late January, the federal government decided to legalize the vigilante movement. So far around 600 people have signed up with the legalized force out of an estimated 20,000 vigilantes.
The Knights Templar, a cult-like gang that claims to be the protector of Michoacan, has accused the vigilantes of working as a proxy force for the rival Jalisco New Generation drug cartel.
Some officials indicated last year that some vigilante groups might have been infiltrated by the Jalisco cartel.
But more recently the vigilantes have been seen as allies of the federal government.
The Knights Templar import drug precursors from Asia to cook crystal meth that they then export to the United States.
The gang has also taken hold of much of Michoacan's economy, demanding protection payments from farmers and shopkeepers as well as extracting iron ore that they then export to China.