A video claiming to be from Mexico's powerful Jalisco New Generation Cartel (CJNG) circulated on social media on Friday, urging that fighting be kept between criminal groups and avoid innocents.
Two Jesuit priests and a tour guide were killed last month in a suspected run-in with a wanted drug trafficker in the border state of Chihuahua, a crime that shocked Mexicans and drew condemnation from Pope Francis.
More than 30,000 people were murdered in Mexico last year, with much of the violence linked to fighting between rival drug trafficking organizations.
"I ask you that the war remains between us, that we don't involve anyone who shouldn't be involved," said a man speaking Spanish in the video, which also showed masked, heavily armed people dressed in combat camouflage.
"We are people who are for the people," the man said.
In the name of the cartel's shadowy leader Nemesio Oseguera Cervantes, alias 'El Mencho', he urged rival cartels across the country to spare doctors, medical personnel and teachers.
Reuters was not able to independently verify the video.
A source familiar with cartel beliefs said it appeared to be real but could not say whether it was the voice of Oseguera.
A press official at the attorney general's office said authorities were analyzing the footage.
Oseguera, a former policeman, has masterminded the CJNG's emergence as a criminal empire spanning five continents and a rival to the Sinaloa Cartel of captured kingpin Joaquin 'El Chapo' Guzman, now in a U.S. prison.
U.S. authorities placed a $10 million bounty on Oseguera's head in 2018.
(Reporting by Lizbeth Diaz and Stefanie Eschenbacher; Editing by Rosalba O'Brien)