MEXICO CITY (Reuters) - The bodies of 23 people were found hanging from a bridge or dismembered in ice boxes and garbage bags in northeastern Mexico on Friday, in an escalation of brutal violence involving rivel drug gangs on the U.S. border.
In a first incident, the bodies of five men and four women were found hanging from a bridge in Nuevo Laredo, in Tamaulipas state just across the border from the Texas city of Laredo.
Police could not confirm who was responsible for the murders but a message seen with the bodies indicated it may have been an attack by the Zetas cartel against the rival Gulf cartel.
Hours later, police found the dismembered corpses of 14 people in garbage bags and ice boxes dumped near the police station of Nuevo Laredo, police investigators said.
They said the second massacre could have been an act of revenge for the earlier killings, police said.
More than 50,000 people have died in drug-related violence in Mexico since President Felipe Calderon launched a crackdown on traffickers after taking office in late 2006 and deployed tens of thousands of federal police and soldiers across Mexico.
The Zeta cartel was founded by desertres from the Mexican special forces who became Gulf cartel enforcers and later split from their employers.
The two gangs are now fighting for control of local drug trafficking routes.
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 and police said the explosion was caused by a grenade.
Discontent over the bloody attacks is helping fuel support for the opposition Institutional Revolutionary Party, or PRI, ahead of Mexico's 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 Sinaloa 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 confrontations in Sinaloa since April 28, a spokesman for local state prosecutors said.
He was unable to specify which gangs were thought to be behind the latest violence in Sinaloa.
(Reporting By Ioan Grillo; Editing by David Brunnstrom)