Suspected cartel hit men gunned down a traffic cop and six young people in a suburb of this northern Mexican metropolis, the State Investigations Agency, or AEI, said.

The assailants wielding automatic rifles and traveling in four vehicles first killed the policeman, identified as 15-year veteran Homero Guajardo Martinez, in a section of the Monterrey suburb of Guadalupe and then rode to a nearby neighborhood and shot dead six young people who were outside a residence, the AEI said in a report.

All of the killings occurred Thursday night.

Home to many of Mexico's industrial giants, Monterrey long seemed immune to the drug war that has claimed more than 40,000 lives nationwide since December 2006, when President Felipe Calderon took office and militarized the struggle with the cartels.

But the metropolis and its suburbs have been battered by a wave of drug-related violence since March 2010.