Bodies found in secret burial pits believed to be victims of drug cartels

Investigators have found 166 skulls in a mass grave in Mexico.

Drones and ground-penetrating radar is being used to search the burial pit in Veracruz on the Gulf coast.

The search began after a tip-off last month.

So far it has yielded 200 pieces of clothing, 144 IDs and personal belongings. Evidence indicated the deaths may have occurred a couple of years ago, Attorney General Jorge Winckler Ortiz said in a statement.

Authorities would not provide details on what may have occurred or where the site is located, given the investigation is ongoing.

Veracruz, along with Nuevo León, Guerrero, Jalisco and Michoacán, are among the states where significant amounts of human remains have been discovered in mass graves.

Cartels such as Los Zetas, El Cartel del Golfo and Cartel Jalisco Nueva Generación have a heavy presence in those states and often use secret burial pits to hide their victims.

Winckler encouraged families with missing relatives to report them to authorities.

More than a year ago in Colinas de Santa Fe, Veracruz, police found nearly 300 remains inside a mass grave.

Non-governmental groups and federal authorities have reported that there are more than 30,000 people reported missing in the country

Maria de Lourdes Rosales Calvo, who has been searching for her son Jonatten Celma Rosales since he was abducted with his girlfriend in July 2013, said the news of the newly discovered grave "gives hope."

"They await us in forensics next week to look at the belongings and IDs that were found," she said.

- with CNN and AAP