Mexico's top human rights official says gangs are re-using clandestine graves, dumping new bodies into burial pits where human remains had already been excavated by authorities.

Mexico's assistant interior secretary says the government is trying to map clandestine burial sites to combat the problem and help families find missing loved ones.

Alejandro Encinas said Tuesday that since President Andres Manuel Lopez Obrador took office on Dec. 1, authorities working with activists and relatives of the missing have found 222 pits and 337 sets of human remains.

The government has budgeted $25 million for the effort, and experts are using forms of ground-penetrating radar and computerized mapping techniques.

Drug and kidnapping gangs often use such pits to dispose of their victims or rivals.