Seven people were found dead on a road in northeastern Mexico in a suspected incident of gangland violence, officials said.

The corpses - all men between 50 and 65 - were found Friday on a rural road in the municipality of San Fernando, the Tamaulipas state Attorney General's Office said.

The bodies bore gunshot wounds and most of the victims had their hands tied. "Shell casings and a high-caliber round were found at the scene," the state AG's office said in a statement.

According to the initial probe, the victims apparently had been killed six hours before their bodies were found.

The grisly discovery was made public after the corpses of nine men were found hanging from a bridge in the Tamaulipas city of Nuevo Laredo, located across the border from Laredo, Texas.

The bodies found in San Fernando bore signs of torture. A message left by the perpetrators of the multiple homicide said the victims were members of the notoriously violent Los Zetas cartel.

The sprawling, mainly rural municipality of San Fernando has been the scene of two of the worst massacres in Mexico's years-long drug war.

A group of 72 Latin American migrants were massacred by the Los Zetas drug cartel in August 2010, apparently after refusing to work for the gang as enforcers or couriers.

The Zetas also were blamed for the massacre of 193 migrants found in 47 clandestine graves between April and June of 2011.

The mass graves were found following reports that gunmen had forced men off buses headed for Reynosa between March 19 and March 31.

The bus passengers were grabbed in a bid to "identify possible members" of the Gulf cartel, which has been battling Los Zetas for control of smuggling routes into the United States, some of the suspects arrested in connection with the killings told investigators.

Friday's slayings came two days after marines captured the Gulf mob's top leader, Jorge Eduardo Costilla Sanchez, alias "El Coss," in the Tamaulipas port city of Tampico, an operation in which not a single shot was fired.

Costilla Sanchez's capture left the Gulf mob - one of Mexico's oldest criminal organizations - without its two top leaders. On Sept. 3, marines captured Mario Cardenas Guillen, alias "El Gordo," who had headed another branch of that drug cartel.

These blows should exacerbate drug-related violence in Mexico, experts say, because the Zetas will look to seize control of areas still under the control of the Gulf cartel, which maintains its stronghold in the northeastern state of Tamaulipas and also operates in other parts of northern Mexico and the country's Gulf coast.

The Gulf cartel and the Zetas, its former armed wing, severed ties in 2010 and that split has sparked turf battles in northeastern Mexico that have left thousands dead.

That region is one of the flashpoints in a nationwide drug war that has left some 60,000 dead since President Felipe Calderon, whose term ends this year, took office in late 2006. EFE