Mexican authorities have arrested 16 municipal police officers accused of protecting drug gang hitmen who massacred people found in mass graves near the U.S. border.
Officials say as many as 126 bodies were discovered near a ranch in Tamaulipas in recent days.
Authorities have blamed the Zetas drug gang for the killings and say 17 gang members have been arrested so far.
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 Calderon took office and launched an offensive against the 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.