Seven people, including three police officers, were killed Thursday in and around this northern Mexican industrial city, the Nuevo Leon state security council said.

Four traffic police were shot early Thursday in the Monterrey suburb of Apodaca, a source on the council told Efe.

Three of the officers died and the fourth, a policewoman, was rushed to a nearby hospital in critical condition, according to the source, who said that men armed with assault rifles fired at the officers from two vehicles.

Two civilians were found shot to death in the neighboring municipality of Benito Juarez, while two other people were gunned down in separate incidents in Monterrey, the source said.

Thursday's killings came a day after six people died in drive-by shootings in Monterrey, Nuevo Leon's capital.

The shooters were "dressed in camouflage gear similar to that used by Mexican marines and were riding in an SUV," said a spokesman for the state security council.

The assailants first killed four individuals in the Constituyentes de Queretaro neighborhood and later two others in the neighboring Fidel Velazquez district.

The attacks occurred Wednesday, just hours after the first unit of a new state police force - which is to have a total of 14,000 members by 2014 - began operating.

Nuevo Leon has seen a sharp uptick in violence involving violent drug cartels, whose turf battles have left more than 1,300 dead over the past 12 months.

Suspected members of the Los Zetas drug cartel killed 52 people on Aug. 25 in an arson attack on an upscale casino in Monterrey, the deadliest attack in years on ordinary civilians in Mexico.

More than 40,000 drug-war deaths have occurred in Mexico during the administration of President Felipe Calderon, who militarized the struggle against the cartels after taking office in December 2006.