MEXICO CITY (AP) — Investigators in northern Mexico said Wednesday they have found six sets of skeletal remains and are performing forensic tests to see if they are some of the 10 men from Mexico’s most persecuted Indigenous group who were abducted in mid-July.

The crime scene in the desert of the northern state of Sonora is likely to be a major embarrassment for President Andrés Manuel López Obrador, who has made it his special project to bring justice to the Yaqui Indigenous community.

The Mexican leader had invited U.S. President Joe Biden to attend a Sept. 28 ceremony to ask forgiveness of the Yaquis for a government campaign to exterminate or exile them around 1900; some Yaquis live in the United States. The U.S. is reportedly sending Secretary of State Antony Blinken instead.

There was no information on the other four missing Yaqui men, who have not been seen since July 15. It may be the largest killing of Indigenous people in Mexico since 15 people were bludgeoned to death in a village dispute in Oaxaca state in 2020.

Sonora state prosecutor Claudia Contreras said relatives had already identified some of the belongings found with the skeletons as those of the missing Yaqui men.

Prosecutors have said there is evidence that drug cartels are preying on the Yaquis. Conteras said that investigators searching for the missing Yaqui men came under fire earlier this week from automatic rifles on the remote hillside near where the skeletons were found.

The investigators returned fire, killing two of the assailants. They then found what appeared to be an encampment of the kind often used by drug cartels, with guns, maps and tactical gear. The skeletons were found almost at surface level nearby.

Prosecutors said one such criminal gang killed a Yaqui rights leader in May. They said the gang killed Yaqui leader Tomás Rojo Valencia because they wanted money his Indigenous group had raised at highway blockades.

Rojo Valencia disappeared May 27 amid tensions over months of periodic blockades the Yaqui put up to protest gas ducts, water pipelines and railway lines that have been run across their territory without consulting them or giving them much benefit. The Yaquis have seen much of the water from their territory piped away by the government to supply nearby cities.

Sonora state prosecutor Claudia Contreras said Rojo Valencia had been trying to install a toll booth on a main highway that runs through Yaqui territory to raise money for his Indigenous community. It was apparently the money that was behind the killing of Rojo Valencia.

But some activists are not convinced.

Alberto Vizcarra, a leader of the Citizen's Movement for Water, said the fight over scarce water may ultimately be behind the killings. “What they did to Tomás (Rojo Valencia) was a political crime,” Vizcarra said.

López Obrador has described as Mexico’s most persecuted Indigenous group, and has started some programs for them. The Yaquis are perhaps best known abroad for the mystical and visionary powers ascribed to them by American writer Carlos Castaneda.

The Yaquis stubbornly fought the Mexican government’s brutal campaign to eliminate the tribe in the late 1800s and early 1900s. But they were largely defeated by 1900, and dictator Porfirio Diaz began moving them off their fertile farmland to less valuable territory or to virtual enslavement on haciendas as far away as the far eastern state of Yucatan.