The 72 people found dead at a Mexican ranch near the U.S. border may have been killed by the Zetas drug cartel, government officials say.

The bodies of 58 men and 14 women were discovered Tuesday when Mexican marines manning a checkpoint on a highway in the northern state of Tamaulipas were approached by a wounded man who said he had been attacked by gunmen at a nearby ranch.

(CBC)

The navy said it dispatched aircraft to check out the man's report and when the gunmen saw the marines, they opened fire and tried to flee in a convoy of vehicles. One marine and three of the suspected gang members were killed in the shootout.

The survivor, who is Ecuadorian, later told investigators he and a group of migrants had been kidnapped by gunmen who identified themselves as members of the Zetas drug gang, said Vice-Admiral Jose Luis Vergera, a spokesman for the Mexican navy.

It was not clear why the 72 victims were killed or whether it happened at the same time. A Mexican official, who spoke on condition of anonymity, said investigators believe the victims were killed within recent days.

Officials are trying to identify the bodies, which were found in a room at a ranch near San Fernando, a town about 160 kilometres south of Brownsville, Texas. They believe the victims were migrants from Honduras, El Salvador, Brazil and Ecuador.

The migrants were trying to reach the U.S. border, reports in the Mexican news media suggest.

The newspaper Reforma, citing a police source, reported that the migrants had refused to pay extortion fees demanded by the armed group. Mexican officials could not immediately confirm the report and have not provided any information about why the migrants were targeted.

Drug gangs often demand payment from migrants trying to cross the border and sometimes kidnap them, holding them hostage while demanding money from relatives in the United States or their home countries.

3rd mass of bodies this year

It was the third time this year that Mexican authorities have discovered large masses of corpses. In the other two cases, investigators believe the bodies were dumped at the sites over a long time.

In May, authorities discovered 55 bodies in an abandoned mine near Taxco, a colonial-era city south of Mexico City that is popular with tourists.

In July, investigators found 51 corpses during two days of digging in a field near a garbage dump outside the northern metropolis of Monterrey. Many of those found were believed to have been rival traffickers. But cartels often dispose of the bodies of kidnap victims in such dumping grounds.

The region has been besieged by a turf battle between the Zetas and their former ally, the Gulf cartel.

Drug violence has surged since President Felipe Calderon, who took office in late 2006, dispatched soldiers and federal police to root out traffickers from their strongholds in northern Mexico and along the Pacific coast.

More than 28,000 people have been killed in drug-gang violence since the offensive began.