Experts sought Thursday to identify the 59 bodies found in mass graves in northern Mexico, as officials came under pressure from rights groups to get its security crisis under control.
"We are conducting autopsies and other forensic studies, and we do not have anything yet that tells us whether there are any foreigners," an official said by telephone from the medical examiner's office in Matamoros, a city near the US border.
The bodies, discovered over the past week in eight illegal mass graves on a ranch in the farming village of La Joya, in northeast Tamaulipas state, were transported to Matamoros in refrigerated containers under police and military escort.
Tamaulipas, bordering the US state of Texas, is one of the most popular routes for migrants trying to reach the United States.
The gruesome discovery was made by a military patrol in San Fernando, the same municipality where 72 migrants from El Salvador, Honduras, Guatemala, Ecuador and Brazil were found dead in August 2010, killed for refusing to work for drug traffickers.
The Tamaulipas prosecutor's office said Wednesday that 11 people had been arrested and another five kidnapping victims had been set free in the same operation, which was launched following a March 25 complaint about the disappearance or abduction of several bus passengers in the area.
The prosecutor's office in a statement said it was "trying to establish if the remains are those of the people who went missing on the buses."
In London on Thursday, rights watchdog Amnesty International called on Mexican authorities to conduct a "full and effective investigation" into the killings, take urgent action to identify the victims, "and bring those responsible to justice."
"The mass graves found yesterday once again show the Mexican government's failure to deal with the country's public security crisis and reduce criminal violence which has left many populations vulnerable to attacks, abductions and killings," said Rupert Knox, Amnesty's researcher on Mexico.
"All too often such human rights crimes have gone unpunished, leaving criminal gangs and officials acting in collusion with them free to target vulnerable communities, such as irregular migrants," he added.
The latest mass grave discovery was announced by Mexican officials on Wednesday, the same day thousands of outraged citizens took to the streets of 38 Mexican cities, venting anger over widespread violence linked to the country's illegal drug trade.
Seven major drug gangs are operating in Mexico and their bloody clashes have left over 34,600 people dead since December 2006, when Calderon's government launched a military crackdown that has so far failed to put a damper on the violence.
Over 3,000 people have been killed this year alone, according to figures cited by the Mexican media.
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