A laborer was killed and a restaurant waiter was wounded when assailants wielding assault rifles shot up business establishments on a main square in Cadereyta, Nuevo Leon, the State Investigations Agency said.

Thursday night’s shooting spree came two days after federal police and soldiers arrested 40 Cadereyta municipal cops on suspicion they were colluding with drug traffickers.

Shortly after midnight Thursday, attackers hurled Molotov cocktails at three auto dealerships in Monterrey, Nuevo Leon’s capital and home to some of Mexico’s leading corporations.

In the neighboring state of Tamaulipas, one gunmen and one soldier were killed Thursday in a three-sided battle involving the military and members of two rival drug gangs.

Troops intervened as contingents from the Gulf and Los Zetas cartels exchanged shots in a commercial district of Miguel Aleman, the defense department said in a statement.

The soldiers captured 11 gunmen, seizing 20 rifles, two handguns, eight grenades, 7,693 rounds of ammunition and four vehicles, according to the statement.

Nuevo Leon and Tamaulipas have been rocked by a war among drug traffickers cartels for control of smuggling routes into the United States.

The violence has intensified since the February 2010 appearance in Monterrey of giant banners heralding an alliance of the Gulf, Sinaloa and La Familia drug cartels against Los Zetas.

The cartels arrayed against Los Zetas blame the group’s involvement in kidnappings, armed robbery and extortion for discrediting “true drug traffickers” in the eyes of ordinary Mexicans willing to tolerate the illicit trade as long as the gangs stuck to their own unwritten rule against harming innocents.

A total of 15,270 people died in drug-related violence in Mexico last year, and more than 36,000 people have died since President Felipe Calderon declared war on the cartels shortly after taking office in December 2006, deploying tens of thousands of soldiers, marines and Federal Police officers across the country.