Mexican authorities Tuesday reported the discovery of 28 more bodies in a northeastern state, bringing to 116 the number of dead unearthed since officials began investigating mass kidnappings of bus passengers.
As horror mounts over the savagery in Tamaulipas, federal officials said they had sent in more troops and would carry out "constant monitoring" of highways in the violence-ravaged border state.
The government of President Felipe Calderon has poured troops into Tamaulipas after previous episodes of grisly violence. But nothing has quelled bloodletting by drug-trafficking gangs that are essentially in control of big swaths of the state.
Mexico's interior minister, Jose Francisco Blake Mora, said criminal gangs were acting out of "desperation." Officials have arrested 17 people in connection with the bodies.
"Organized crime, in its desperation, resorts to committing extraordinary atrocities that we cannot and should not tolerate," Blake said after meeting with Tamaulipas Gov. Egidio Torre Cantu in Mexico City.
Before Tuesday, a series of mass graves found within a week in rural San Fernando had yielded 88 bodies, amid reports that gunmen were stopping buses and seizing passengers.
Authorities suspect the Zetas gang, which was blamed last year in the kidnapping and killing of 72 migrants from Central and South America in the same area of Mexico after trying to force them to work for the group.
Mexican authorities have not spelled out any motive for the bus attacks on a highway that leads to the U.S. border, 90 miles to the north. The region is traversed by thousands of Mexican and Central American migrants seeking work in the U.S.
Migrants crossing Mexico are often targets of robbery or attempts to extort money from loved ones in the U.S. or back home.
A chilling byproduct of the ruthless drug war in Mexico that has killed more than 34,000 people in more than four years is the disappearance of thousands of people, as The Times reported last month.
Officials had said they believed that most of the unearthed victims were Mexican, but only a few have been identified. The Guatemalan government said at least one of the dead was from Guatemala.
Coroner's officials have taken DNA samples from 72 victims to check if they match those of dozens of people from the central states of Guanajuato and Queretaro who were reported missing after heading north. A U.S. citizen is believed to be among those seized from buses.