Monterrey (Mexico) (AFP) - A mass grave has been found in northern Mexico, authorities said Tuesday, as a rights group indicated it could contain 31,000 bone fragments corresponding to at least 31 bodies.

The pit was discovered on a ranch in the town of Salinas Victoria, some 35 kilometers (22 miles) north of the industrial hub of Monterrey, said a spokeswoman for the Nuevo Leon state prosecutor's office, Priscila Rivas.

"The ranch was found through statements by detained criminals, information from victims and investigations by the prosecutor's office," Rivas told AFP.

The spokeswoman declined to say how many pieces of bones were unearthed or how many bodies they could represent.

But Consuelo Morales, who heads the Citizens Supporting Human Rights (CADHAC), said authorities told her organization that 31,000 bone fragments were found since the grave was detected earlier this year.

"The genetic profiles of 31 people have already been identified. It's what the prosecutor's office told us," said Morales, whose group represents relatives of missing people.

She said that her organization had told the authorities back in January that the ranch named "Las Abejas" (The Bees) may contain a clandestine grave. The fragments have been found over the course of several months.

Authorities have cordoned off the ranch as they continue to search for remains, objects or pieces of clothing that could help identify the victims.

The bones have been taken to the University Hospital of Monterrey, where DNA tests are being conducted, Morales said.

Mexican drug cartels often dump the bodies of their victims in mass graves. In 2013, for instance, 64 bodies were unearthed between the western states of Jalisco and Michoacan.

Nuevo Leon state has been the scene of brutal turf wars between the Zetas and Gulf cartels in recent years.

Tens of thousands of people have been killed across the country since the drug war intensified in 2006, while 20,000 more have disappeared.