Mexican authorities have pulled about 30 more bodies from an unmarked mass grave in the northern part of the country.
Officials say the bodies were found near the city of Durango, capital of the state with the same name.
The discovery comes after authorities recently unearthed mass graves holding as many as 126 bodies in the northwestern state of Tamaulipas near the U.S. border.
Authorities have arrested at least 17 members of the Zetas drug gang for the killings, as well as 16 municipal police officers accused of protecting those who carried out the killings.
Migrants trying to reach the United States often cross through Tamaulipas. The state is where 72 Central American migrants were found shot to death last August. The Zetas have been blamed for that massacre as well.
Drug-related killings have claimed at least 35,000 lives since 2006, when President Felipe Calderón took office and launched an offensive against drug cartels.
The Zetas began as a Mexican military unit that defected and began working with the Gulf cartel, based in Juarez, Mexico, across the Rio Grande river from the U.S. city of El Paso, Texas. The Zetas split from the Gulf cartel last year. The two groups are now fierce rivals.