Manhunt for killers of 72 migrants
Heavily armed patrols in armored personnel carriers, trucks and jeeps swept though towns and cities in the border region while helicopters buzzed overhead a day after the bodies of 72 people were found at a remote ranch. The victims, believed to be Central and South American migrants, appear to have been blindfolded and bound before they were lined up against a wall and gunned down.
Photographs showed bodies heaped on the ground at the ranch in Tamaulipas state, the scene of some of Mexico's worst drug violence as the Gulf cartel and a spinoff group, the Zetas, fight over smuggling routes.
Migrants trying to slip into the United States are increasingly at risk of kidnapping and extortion by drug gangs that operate with near impunity in parts of northern Mexico, police and analysts say.
More than 28,000 people have died in drug violence since president Felipe Calderon launched his war on the cartels when he took office in late 2006.
Mr Calderon has vowed to push ahead with the crackdown, but has warned that more violence is likely to lie ahead.