The governor of Nuevo Leon state, on the Texas border, on Wednesday asked the army to man road checkpoints following a string of killings this week that appear to be linked to a bloody turf war between rival drug gangs.

Gov. Natividad Gonzalez's request came hours after at least two assailants shot a man to death during daylight hours at a car wash in the state capital of Monterrey. Police said they did not know the identity of the victim, who was shot four times.

On Monday, Monterrey police found two corpses, including one that had been decapitated. The day before, at least 15 gunmen shot at the car of federal investigator Veronica Palacios, seriously wounding her and killing a female passenger.

"(We're asking) for reinforcement in some checkpoints, especially those on the highways leading to Coahuila and Tamaulipas and in some other areas in the state," Gonzalez told reporters.

Army checkpoints searching primarily for weapons and drugs are already used in several Mexican states, including neighboring Tamaulipas, where there have been more than 100 drug-related killings this year.

Soldiers also regularly accompany federal agents in raids against drug traffickers nationwide.

Monday's decapitated victim has been identified as 17-year-old Julio de Leon of Nuevo Laredo, across the Rio Grande from Laredo, Texas. Next to the body were two notes addressed to reputed drug lord Joaquin "El Chapo" Guzman of the Sinaloa Cartel.

Investigators say the Sinaloa Cartel is fighting the Gulf Cartel for billion-dollar drug smuggling routes into the United States. The battle has led to beheadings, grenade attacks and execution-style killings across Mexico. A hot spot has been Nuevo Laredo, where slayings have occurred almost daily this year.

Gonzalez said that Nuevo Laredo drug smugglers may be moving to Monterrey to hide from rivals looking to kill them.

"Monterrey, after Mexico City, is one of the biggest cities and obviously they are looking at this city as a haven," Gonzalez said.