Gunmen murdered four people, including two police officers, in two attacks in the northern Mexican city of Monterrey, while the security forces killed five gunmen in a shootout in the western state of Jalisco, officials said.

Men armed with large-caliber weapons opened fire Monday on a police patrol car in the southern section of Monterrey, the capital of Nuevo Leon state, killing an officer, the state Security Council said.

Gunmen staged a simultaneous attack on an officer at a food stand outside the police headquarters in the eastern section of Monterrey, killing him.

Two men eating with the officer were also killed in the shooting, officials said, adding that one of the men may be a police officer.

Monterrey, Mexico's most important industrial city, and its suburbs have been battered by a wave of drug-related violence since March 2010, when three rival cartels reportedly went to war with Los Zetas.

Los Zetas has been battling an alliance of the Gulf, Sinaloa and La Familia drug cartels, known as the Nueva Federacion, for control of the Monterrey metropolitan area and smuggling routes into the United States.

Heriberto Lazcano Lazcano, known as "El Lazca," deserted from the Mexican army in 1999 and formed Los Zetas with three other soldiers, all members of an elite special operations unit, becoming the armed wing of the Gulf drug cartel.

After several years on the payroll of the Gulf cartel, Los Zetas, considered Mexico's most violent criminal organization, went into the drug business on their own account and now control several lucrative territories.

A total of 267 murders were registered in the industrial city in 2009, with the figure rising to 828 in 2010 and more than 900 so far this year, official figures show.

Army troops and state police, meanwhile, killed five gunmen and arrested 12 others in a shootout in Mexquitic, a city in the western state of Jalisco, federal security officials said.

Three other gunmen, who were carrying five kilos of cocaine and nearly 300,000 pesos (about $25,500), were arrested in the northeastern state of Tamaulipas.