Mexico City, Mexico (CNN) -- Authorities in the Mexican border state of Nuevo Leon have finished excavating and are trying to identify 51 bodies they found in nine hidden mass graves, state media said.

The graves could be connected to drug gang violence, Nuevo Leon Governor Rodrigo Medina de la Cruz told the state-run Notimex news agency.

Investigators found charred remains, incinerated bone fragments and stains of fire on the ground where bodies were presumably burned in steel drums, Notimex said.

Teams from the state attorney general's office and the Mexican army used dogs and heavy machinery in their 72-hour search of the area, Notimex reported Saturday.

Investigators believe some of the bodies had been dumped within the past 15 days, said Alejandro Garza y Garza, Nuevo Leon attorney general.

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 mass graves 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.

Nuevo Leon, which borders Texas, has seen a spike in drug violence this year due to an intensifying rivalry between former partners: the Gulf cartel and a group know as the Zetas.