Four police officers and a doctor have been killed in separate attacks in and around the northern Mexican city of Monterrey, authorities said, Press TV reported.
Unidentified assailants threw a grenade and fired at a police station in the town of Valle Verde on Thursday.
Two officers and a doctor, who was in the police station, were killed in the attack, said Jorge Domene, security spokesman for Nuevo Leon state, which borders the United States.
Domene said in a news conference that a female police officer was also killed in an attack on her patrol car in the nearby town of Guadalupe and another police officer was shot dead at a road junction.
"Yesterday's events clearly represent acts by organized crime trying to intimidate or reverse the actions that authorities have taken ... to counter the violence that has been unleashed in our state," Domene noted.
Police are investigating any affiliation between the killers and the local drug gangs.
Nuevo Leon and the neighboring Tamaulipas state have recently observed some of Mexico's worst drug violence.
Since December 2006, when Mexican President Felipe Calderon ordered an armed onslaught on the country's powerful drug cartels, more than 30,000 people have been killed.