A total of 23 bodies have been found hanging from a bridge or dismembered in ice boxes and garbage bags in northeastern Mexico, in an escalation of brutal violence involving rival drug gangs on the US border.
Bodies of five men and four women were found on Friday 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.
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 deserters 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 favourite 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.
In Veracruz, grieving, frightened journalists remembered three slain colleagues on Friday as members of a press corps working under terrifying conditions.
Traffic dwindled from the streets and shopping areas emptied hours after the discovery Thursday afternoon of Guillermo Luna Varela, Gabriel Huge, Esteban Rodriguez and Irasema Becerra, who had been slain, dismembered and stuffed into black plastic bags dumped into a waste canal.
It was a sense of dread familiar to Veracruz, where a cartel battle for control of one of Mexico's largest ports has spawned horrors such as the slaughter of 35 people dumped on a main highway in rush-hour traffic in September.
At least seven current and former reporters and photographers have been slain in Veracruz over the last 18 months, forcing their surviving colleagues to work under precautions reminiscent of those in a war zone.
Journalists let colleagues and family know by phone when they are leaving for work and coming home. They call ahead before covering a story to see if the area is safe.
Once they go, they move in groups of four or five and scan areas from the vehicle before getting out, remaining in constant contact with their newsroom.