The bodies of 23 people, hands bound and with gunshot wounds, have been found in the arid 'hot land' of western Mexico that for the past year has formed a battleground for drug cartels, vigilantes and security forces.
Nine of the bodies were found on an abandoned property near the town of Buenavista Tomatlan, along with a sign indicating they may have been members of the Knights Templar cartel, said prosecutor's spokesman Alejandro Arellano.
He said the sign left alongside the bodies read: "For those who continue to support the Knights Templar, we are here, united."
The notice was signed with the initials of a rival cartel, the Jalisco New Generation, as well as the initials G C, indicating another vigilante group.
The Knights Templar have sought to control the territory near the Jalisco state border through killings and extortion, but have met violent opposition from the New Generation and vigilante groups.
The bodies were found in the lawless neighbouring states of Michoacan and Guerrero, in the arid Tierra Caliente region, or Hot Land, where the government has struggled to rein in the violence.
A total of 14 bodies were found in Guerrero, eight of them in San Miguel Totolapan in the Tierra Caliente, and six in a mass grave near the town of Taxco, said state government spokesman Jose Villanueva Manzanarez.
In San Miguel Totolapan, five bodies were found in the back of a Ford pick-up truck. All were clothed in military fatigues, and armed with heavy weapons and grenades, Manzanarez said.
Three more young men were found elsewhere in the same town. They had also been shot.
Many of the bodies were badly decomposed.
Thousands of troops were sent into the area in May in an attempt by President Enrique Pena Nieto to wrest control of the state from the cartels
Residents initially welcomed the deployment, while some vigilante groups agreed to lay down their arms.
But last month, the Knights Templar launched counter-attacks on police, killing four officers.
One of Mexico's highest-ranking navy officers was also killed along with his bodyguard last month on an isolated road in Michoacan.
In a separate development on Saturday, the army said it had captured one of the leaders of the country's infamous Gulf cartel.
Mario Armando Ramirez Trevino was arrested in the town of Rio Bravo near the US border, in a major operation in which helicopters were deployed.
The Gulf cartel controls most of the cocaine and marijuana trafficked through the Matamoros corridor and across the Texan border.
It is the second arrest of a major drug boss since President Peña Nieto took office in December, and follows the capture of Miguel Angel Trevino Morales, alias Z-40, the leader of the brutal Zetas cartel, in July.