Seventeen men and three women were shot dead inside the protest site in Las Tinaya, west coastal state of Michoacan – one of the most illegal areas in Mexico – on Sunday.
All the victims were shot and the last of them died on the way to the hospital, authorities said.
Four people are being treated for injuries.
The perpetrators apparently planned the shooting and got into a stolen truck belonging to a snack company, according to prosecutors in Mitsoakan.
Image: Army officers and prosecutors arrived at the scene after the shooting. Photo: AP Image: Investigators at the scene where 20 people were killed
“The snack truck arrived and several gunmen in camouflage clothes came out,” a statement from prosecutors said.
“At the same time, a bus outside the building was used as a blockade, apparently to prevent the victims from escaping or calling for help,” the statement said.
Investigators found 15 vehicles apparently belonging to the victims, one of which bore stickers with the logo of a criminal gang.
Prosecutors said drug cartels and other criminal gangs were fighting in the area.
“There are indications that the attack involved a confrontation between criminal groups,” the federal Department of Public Safety said in a statement.
Image: Police went down to the scene of the hidden cockfight after the shooting. Photo: AP
“It was a massacre of one group by another,” Mexican President Andres Manuel Lopez Obrador told a regular news conference, expressing his sorrow over the deaths.
He blamed criminal gangs in the area for the killings and said a group was on its way to investigate the crime.
Las Tinaya has seen increasing violence as the powerful Jalisco New Generation cartel fights local gangs for control of drug routes.
The battles involved the use of bomb drones, landmines and improvised armored vehicles.
Gang violence has driven record levels of assassinations since President Obrador took office in late 2018, pledging to reduce organized crime using a less “confrontational approach.”
However, widespread problems persisted, and average annual homicides are well on their way to being the highest in any Mexican administration since modern records began.
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Last month, the United States temporarily suspended avocado shipments from Michoacan after inspectors threatened to kill them.
Avocado growers in the state – the only one in Mexico that is fully authorized to export to the US market – face blackmail due to ongoing battles with drug cartels near their farms.
Cockfighting, although illegal in many areas, remains a popular hobby in parts of Mexico.
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