TUCSON, Ariz. – The number of bodies recovered from a mass grave in Mexico near the Arizona border has risen to 42 after three days of searching, the Sonora attorney general's office said.

A group of Mexican mothers who belong to the group Madres Buscadoras de Sonora, or Searching Mothers of Sonora, discovered the mass grave Thursday near the beach resort town of Puerto Peñasco, commonly known in Arizona as Rocky Point.

Staff members from the attorney general's office, as well as forensic workers from the state's criminal investigations unit, joined the mothers in their search. They will help transport the bodies to a lab and identify the remains.

The women found 13 bodies on Thursday, fully clothed. On Friday, they found an additional 14 bodies, according to state officials. More bodies were uncovered Saturday.

The identities of the dead were not known, and it was unclear how long the remains had been buried.

Lupita Orduño, spokeswoman for the state's attorney general's office, said Thursday that it was too early to speculate why the bodies were buried in a mass grave because officials first had to determine how the people died.

"We're just now trying to identify the cause of death," she said. "We don't know how they were killed. And that's what the forensic lab will do."

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At least two of the bodies were still in a stage of decomposition, meaning they were buried recently. The remaining bodies were largely skeletal remains, indicating they had been there longer. At least two of them could be women, the state added.

The group has not responded to requests for comment on the discovery. But a post on their Facebook page from Wednesday alluded to the discovery of the mass grave in Rocky Point on that day.

The Searching Mothers of Sonora describe themselves as "mothers searching for missing persons or human remains, to bring peace to other families that are going through the same pain," according to their Facebook page.

"We are not looking for the perpetrators, we just want back what was taken from us one day," their description said.

The Attorney General's Office encouraged the relatives of missing loved ones in the area to file missing person reports and submit their DNA to a national database so they can better identify the remains found.

Forensic workers will remain in Puerto Peñasco to help collect samples from relatives, setting up hours on Saturday for that task.

"We will continue working, shoulder to shoulder, with the searching mothers of Puerto Peñasco. Their pain makes them strong, and supporting their brave labor is an act of justice that we directly assume at the Attorney General's Office of Sonora and the National Search Commission," said Claudia Indira Contreras Córdova, the attorney general for Sonora.

Puerto Peñasco, about a three-hour drive southwest of Phoenix, has been a relatively safe haven in the past few years, in an area that is otherwise known as a busy, and very profitable, drug and human smuggling route into Arizona.

But there has been an occasional cartel-related gunfight over the years. The city was the scene of especially heavy fighting among criminal groups and the Mexican military in the early 2010s.

Recently, the Sonoran state government, with the help of Arizona officials, has invested greatly in improving safety in and around the beach resort town, as well as the main highway from Arizona leading to the city.

The city is a key source of tourism revenue for the state, but an increasing number of visitors come from Arizona, making it a priority for both states.

Follow Rafael Carranza on Twitter: @RafaelCarranza.