MEXICO CITY — More than 250 skulls have been found over the last several months in what appears to be a drug cartel mass burial ground on the outskirts of the city of Veracruz, prosecutors said Tuesday.

Veracruz state’s top prosecutor, Jorge Winckler, said the clandestine pits appeared to contain remains of cartel victims killed years ago.

The news came as no surprise to Lucia Diaz, one of the mothers of people who have disappeared whose group is known as Colectivo Solecito.

The mothers pushed authorities to investigate the fields where the skulls were found because they suspected more than a year ago that the wooded area known as Colinas de Santa Fe was a secret burial ground.