Suspected drug gang killers dumped the mutilated bodies of 49 people on a highway near the northern city of Monterrey in one of the worst atrocities to hit Mexico in recent years.

The mutilated corpses were found stuffed into bags in the early hours of Sunday on a highway in the municipality of Cadereyta Jimenez, officials from the state of Nuevo Leon told Reuters.

It was not immediately clear who the victims were. A forensic investigator at the scene said some of the bodies showed signs of decay, indicating that they may have been dead for days.

Nuevo Leon state Attorney General Adrian de la Garza told the Associated Press he did not rule out the possibility that the victims were U.S.-bound migrants.

The bodies of the 43 men and six women were found in the town of San Juan on the non-toll highway to the border city of Reynosa around 4 a.m., forcing police and troops to close off the highway. Nuevo Leon state security spokesman Jorge Domene said at a news conference that a banner left at the site bore a message with the Zetas drug cartel taking responsibility for the massacre. 

Domene said the fact the bodies were found with the heads, hands and feet cut off will make identification difficult. The bodies were being taken to Monterrey for DNA tests.

De la Garza said the victims could have been killed as long as two days ago at another location, then transported to San Juan, a town in Cadereyta municipality, about 105 miles west-southwest of McAllen, Texas, or 75 miles southwest of the Roma, Texas, border crossing.

It was the latest in a string of mass slayings that have convulsed Mexico over the past few months, many of them concentrated in the north of the country, where the brutal Zetas drug gang has waged a bloody war for control of smuggling routes.

President Felipe Calderon staked his reputation on bringing Mexico's drug gangs to heel, sending in the army to fight them shortly after taking office in December 2006.

Since then, however, the violence has spiraled, and more than 50,000 people have fallen victim to the conflict.

The violence has eroded support for Calderon's conservative National Action Party (PAN), which looks likely to lose power when Mexico elects a new president on July 1. The constitution prevents Calderon from seeking a second term in office.

The Nuevo Leon government official said the killings appeared to be the work of drug cartels and that a message of the kind often favored by the gangs had been left at the scene. But it was not clear who was responsible.

The Zetas have been locked in a bloody conflict with other gangs, including the Gulf cartel.

Last Wednesday, 18 people who were found decapitated and dismembered near Mexico's second-largest city, Guadalajara.

A week earlier, the bodies of nine people were found hanging from a bridge and 14 others found dismembered in the city of Nuevo Laredo, just across the U.S. border from Laredo in Texas.

Late last year, several mass killings took place in the eastern state of Veracruz, which has been ravaged by the Zetas.