By Mica Rosenberg
MEXICO CITY (Reuters) - Nine bodies, some bound and blindfolded, were found hanging from a bridge over a highway in northeastern Mexico early on Friday, in an escalation of brutal attacks right on the U.S. border where rival drug gangs are fighting for control.
The victims were five men and four women, said the police in Nuevo Laredo, in Tamaulipas state just across the border from Laredo, Texas. Police could not confirm who was responsible for the gruesome murders but a message found with the bodies indicated it may have been an attack by the Zetas cartel against the rival Gulf cartel.
The Zetas were founded by Mexican special forces deserters who started out as Gulf cartel enforcers, though they later split from their employers, and the two gangs are now fighting for control of local drug trafficking routes.
Tamaulipas has exploded in violence due to the feud.
Last month the dismembered remains of 14 men were found stuffed inside a minivan left near Nuevo Laredo's town hall. Days later a car exploded outside police headquarters.
Local police said the explosion was caused when a grenade was thrown into the car.
More than 50,000 people have died in drug-related violence since President Felipe Calderon launched a crackdown on the traffickers after taking office in late 2006, deploying tens of thousands of federal police and soldiers across Mexico.
Discontent over the bloody attacks is helping fuel support for the opposition Institutional Revolutionary Party, or PRI, ahead of a July 1 presidential election.
Opinion polls make the PRI the favorite to regain the presidency they held for most of the past century.
The Zetas have also been engaged in hostilities with the powerful Sinaloa cartel, named after the state in northwestern Mexico where violence has surged over the past week.
Sinaloa is the home turf of Mexico's most wanted drug trafficker, Joaquin "Shorty" Guzman, who heads the cartel, and analysts say his killing or capture would boost Calderon's embattled conservatives ahead of the presidential vote.
Calderon cannot seek a second term in office.
At least 20 suspected drug gang members, one police officer and a soldier have been killed in six stand-offs in Sinaloa since April 28, said a spokesman for local state prosecutors.
He was unable to specify which gangs were thought to be behind the latest violence in Sinaloa.
(Additional reporting by Lorne Matalon; Editing by Eric Beech)