(CNN) -- Police discovered Sunday the remains of five men discarded along the highway between Monterrey and Reynosa, in northern Mexico, Notimex reported. The state news agency said the bodies were naked, except for plastic bags.
In other violence, gunmen clashed with soldiers in three separate incidents in the northern Mexican state of Tamaulipas, leaving 13 people dead, the agency reported Saturday.
In the first, in San Fernando, gunmen opened fire on a group of soldiers as they were making their rounds, Notimex reported. The news agency said the soldiers responded in kind, leaving six people dead.
The second incident, in Valle Hermoso, was reported much the same. Soldiers on patrol came under gunfire and they responded, leaving six people dead, Notimex reported.
In the third incident, in Nuevo Laredo, soldiers again came under attack and killed one of their assailants, according to Notimex. The agency added that a second man was arrested.
Separately on Saturday, Notimex reported that the remains of the man in charge of security at a prison in the northern city of Monterrey were found inside a parked car near the jail. Francisco Martinez Ramirez, 60, had been abducted from his home Friday, Notimex said.
The clashes are the latest in a string of violence fueled by the lucrative drug trade in Mexico. According to the government, there have been more than 34,600 drug-related deaths since President Felipe Calderon began a crackdown on the cartels in December 2006.