|Officers found 72 murdered migrants at another site in San Fernando last August [AFP]
At least 59 bodies have been found in a series of pits in the northern Mexico state of Tamaulipas, near the site where suspected drug gang members massacred 72 migrants last summer, authorities said.
The bodies are being examined to determine whether they were bus passengers who were reportedly abducted on March 25, the Tamaulipas state government said in statement on Wednesday in which it "energetically condemned" the crimes.
The pits were found in the farm hamlet of La Joya in the township of San Fernando, in the same area where the bodies of 72 migrants, most from Central America, were found shot to death on August 24 at a ranch.
The victims in the August massacre were illegal immigrants from El Salvador, Honduras, Guatemala, Ecuador and Brazil.
Authorities blamed the killings on the Zetas drug gang, which is fighting its one-time allies in the Gulf cartel for control of the region.
An Ecuadorean and Honduran survived the attack, which Mexican authorities say occurred after the migrants refused to work for the cartel.
Mexican drug cartels have taken to recruiting migrants, common criminals and youths, Mexican authorities say.
Drug gunmen also operate informal checkpoints on highways in Tamaulipas and other northern states, where they hijack cars and rob and sometimes kill drivers.
Protests against violence
The wave of drug-related killings, which has claimed more than 34,000 lives in the four years since the government launched an offensive against drug cartels, drew thousands of protesters into the streets of Mexico's capital and several other cities on Wednesday in marches against violence.
Many of the protesters said the government offensive has stirred up the violence.
"We need to end this war, because it is a senseless war that the government started," said protester Alma Lilia Roura, 60, an art historian.
Several thousand people joined the demonstration in downtown Mexico City, chanting "No More Blood!" and "Not One More!"
A similar number marched through the southern city of Cuernavaca.
Parents marched with toddlers, and protesters held up signs highlighting the disproportionate toll among the nation's youth. "Today a student, tomorrow a corpse," read one sign carried by demonstrators.
The marches were spurred in part by the March 28 killing of Juan Francisco Sicilia, the son of Mexican poet Javier Sicilia, and six other people in Cuernavaca.