At least 49 mutilated bodies were found on the side of a highway in Cadereyta, a city in the northern Mexican state of Nuevo Leon, police said.
The bodies of the victims, six of whom are women, were dumped on the shoulder of the highway to Reynosa, a city in the neighbouring state of Tamaulipas.
Some of the bodies were stuffed into black plastic trash bags while others were left uncovered, Federal Police spokesmen told EFE Sunday.
The bodies were found near the exit to San Juan, a town in Nuevo Leon.
The killers left a banner with the bodies, which were dumped in front of a monument at the entrance to the town.
The message on the banner, which was pulled down by army troops, was not revealed, but the killers spraypainted "100 % zetas" on the monument.
Army soldirs, federal police officers, state police and municipal police officers were mobilized after the discovery of the bodies early Sunday.
Police and soldiers have closed down the highway to allow investigators to gather evidence and remove the bodies.
Police received a call early Sunday that bodies had been dumped on the side of the road, police spokesmen at the crime scene said, adding that most of the corpses were in plastic trash bags.
The Los Zetas drug cartel has been battling the Gulf cartel for control of smuggling routes from Nuevo Leon into the US.
A total of 324 murders were registered in Nuevo Leon in the first two months of this year, a record for a two-month period in the state.
The wave of drug-related violence in Nuevo Leon claimed the lives of 2,003 people in 2011, official figures show.
Heriberto Lazcano Lazcano, known as "El Lazca", deserted from the Mexican army in 1999 and formed Los Zetas with three other soldiers, all members of an elite special operations unit, becoming the armed wing of the Gulf drug cartel.
After several years on the payroll of the Gulf cartel, Los Zetas, considered Mexico's most violent criminal organization, went into the drug business and now control several lucrative territories.
Los Zetas has been blamed for several massacres in recent years.
The cartel was accused of staging the Aug 23, 2010, massacre of 72 migrants, the majority of them from Latin America, at a ranch outside San Fernando, a city in Tamaulipas.
Los Zetas has also been blamed for the massacre of 27 peasants in May 2011 at a ranch in Guatemala's Peten province, which borders Mexico and Belize.
Zetas gunmen set fire to the Casino Royale in Monterrey, the capital of Nuevo Leon, on Aug 25, 2011, killing 52 gamblers and employees, most of whom died of smoke inhalation.