Gunmen dressed in military fatigues killed six people in drive-by shootings in this northern Mexican industrial city, officials said.

The members of the armed group were "dressed in camouflage gear similar to that used by Mexican marines and were riding in an SUV," said a spokesman for the security council of Nuevo Leon state, whose capital is Monterrey.

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.

Elsewhere, at least four suspected hit men linked to the Los Caballeros Templarios/La Familia cartel were killed in a shootout with federal police outside the western city of Ciudad Hidalgo, Mexico's Public Safety Secretariat said Wednesday.

The clash occurred after police tried to inspect a vehicle that had the appearance of a police car, the secretariat said.

It added that the suspects, who were wearing imitation federal police uniforms and were armed with AK-47 assault rifles, opened fire on the officers after noticing their presence.

Spokespersons with the secretariat told Efe that following the shootout the police rescued five people - two adults and three minors - who had been held captive at two houses on an extensive property where the car was discovered.

The first victim was a 60-year-old woman who had suffered only slight injuries but required medical assistance after showing signs of a nervous breakdown.

Four other kidnap victims - an adult and three minors who had been held since Sept. 7 - were rescued from another house located some distance away in the nearby town of Agostitlan.

Police warned citizens that drug gangs may be using fake police cars to commit crimes and urged them to report those vehicles to the authorities via a special hotline.

La Familia used to be the dominant criminal gang in Michoacan but it has been battered by the arrest or death of its top leaders in recent months and the emergence of a splinter group calling itself Los Caballeros Templarios that has seized control of the drug business in that region.

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.