Mexican troops fanned out in the remote countryside near the Texas border as they hunted the perpetrators of the worst massacre in the country's escalating drug war.
With helicopters overhead, heavily armed patrols in armoured personnel carriers, trucks and jeeps swept though towns and cities in the border region a day after the bodies of 72 people were found in an empty building at a remote ranch.
The victims, Central and South American migrant workers, appeared to have been blindfolded and bound before they were lined up against a wall and gunned down.
Photographs showed bloodstained bodies heaped on the ground at the ranch in Tamaulipas state, which has become the scene of some of Mexico's worst drug violence as the Gulf cartel and a spinoff group, the Zetas, fight over smuggling routes.
Officials said investigators were still examining the scene, about 150km from the Texas border, as many of the victims had no identification documents. They had not yet removed all the bodies, which may be flown to state capital Ciudad Victoria.
The United States condemned the "heinous crimes" and offered its support in the drug war. "They are dangerous, they are attempting to undermine the democratic institutions of Mexico, and that's why we pledge to . . . defeat these cartels," State Department spokesman PJ Crowley said in Washington.
The sole survivor of the massacre, an Ecuadorean man, escaped the ranch on Monday after being shot, and told authorities about the killings. He said his fellow victims included Brazilians, Hondurans, Salvadoreans and Guatemalans.
Diplomats from Brazil, Ecuador, El Salvador and Honduras flew to the crime scene yesterday. Central and South American nations condemned the massacre and Ecuador said it was urging Mexico to protect the survivor, Luis Freddy Lala Pomavilla.
Migrants trying to slip into the United States from Mexico are increasingly at risk of kidnapping and extortion by drug gangs that operate with impunity in parts of the country's northern reaches, police and analysts say.
Security forces were fired on when they approached the ranch on Tuesday, and in the ensuing firefight marines killed three gunmen and arrested another. Several suspects escaped.
More than 28,000 people have been killed in drug violence since President Felipe Calderon began his war on the cartels when he took office in 2006. Mr Calderon has vowed to push ahead with the crackdown but has warned of more violence ahead.
A military source in Tamaulipas said the Zetas, a brutal gang led by Heriberto Lazcano, a former Mexican soldier known as "the Executioner," were behind the killings.
Reuters