Story highlights "This is not an attack against the civilian population," a security official says

The bodies were decapitated and dismembered, officials say

The find comes days after a retired military general took charge of the local police

Officials have not ruled out the possibility that victims could be immigrants

Mexican authorities found at least 49 decapitated and dismembered bodies along a highway in a northern border state Sunday morning, officials said.

The remains were left along the road in Nuevo Leon state, between the cities of Monterrey and Reynosa.

A message written on a wall nearby appeared to refer to the Zetas drug cartel.

"This continues to be violence between criminal groups. This is not an attack against the civilian population," said Jorge Domene, Nuevo Leon's state security spokesman.

He said it appeared as though the victims were killed a day or two ago, somewhere else, and that their bodies were then dropped off.

Officials said they had not ruled out the possibility that the victims could be Central American immigrants or residents of another state, telling reporters Sunday that there had not been many local missing persons reports in recent days.

But the area has become a battleground for a brutal conflict between the Zetas and the Gulf cartel, and reports of forced disappearances have become increasingly common in recent years.

Police and troops were combing the area and set up checkpoints after authorities received a report of the remains around 3 a.m. Sunday, police said.

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The remains were found in the municipality of Cadereyta Jimenez, near the industrial city of Monterrey and about 80 miles southwest of the U.S. border, police said.

The middle-class, industrial community where the remains were found is known for a broom factory, an oil refinery and its historic role as one of the first places baseball was played in Mexico.

Last week, a retired military general arrived to take over the city's depleted police force.

At least five municipal employees were slain there last month, the state-run Notimex news agency reported.

Federal forces have stepped up security in Nuevo Leon and the neighboring state of Tamaulipas since November 2010.

More than 47,000 people have been killed in drug-related violence throughout Mexico since President Felipe Calderon announced a crackdown on cartels in December 2006.

Nuevo Leon and Tamaulipas are among the most violent, according to government statistics.

In Monterrey, Nuevo Leon's capital, nearly 400 deaths in 2011 were connected to organized crime -- more than three times the number of people slain in drug-related violence there in 2010.

Among the most high-profile violence in the region was an attack on a casino in Monterrey last August that left 52 people dead. Authorities have said members of the Zetas cartel were behind that attack.

The Zetas started with deserters from the Mexican Army and quickly gained a reputation for ruthless violence as the armed branch of Mexico's Gulf cartel. The partnership ended in 2010, and turf battles between the rival cartels are common in northern Mexico.