(CNN) -- Authorities in the Mexican border state of Nuevo Leon are investigating after finding at least 38 bodies in nine hidden mass graves, the state's attorney general said.
Investigators believe some of the bodies had been dumped within the past 15 days, said Alejandro Garza y Garza, Nuevo Leon attorney general.
State-run news agency Notimex reported that investigators found charred remains, incinerated bone fragments and stains of fire on the ground where bodies were presumably burned in steel drums.
Garza said Friday that the bodies were in an area spanning 3 hectares (about 7 acres) in the municipality of Juarez outside the state capital of Monterrey. Investigators were still searching for additional graves Friday, he said, according to Notimex.
The bodies were mostly males between ages 20 and 50, Notimex said, and many of them had tattoos.
Forensic investigators are performing DNA tests to identify the victims, Notimex reported.
Similar graves sites have been discovered in the Mexican states of Tamaulipas, Guerrero and Quintana Roo since late May. Authorities have linked them to Mexico's ongoing drug war.