Six people were gunned down in the southern section of Monterrey, the capital of the northern Mexican state of Nuevo Leon, police said.

The killing started on Monday in the San Angel neighborhood, where gunmen opened fire with AK-47 assault rifles on a man.

The gunmen went to a taxi stand in the Estanzuela area a few minutes later and murdered a woman and four cabbies.

The shooting occurred near where gunmen killed four taxi drivers last Thursday.

The gunmen belonged to the Los Zetas drug cartel, which has been targeting people who have links to the rival Gulf cartel, the police spokesman told Efe on condition of anonymity.

Gunmen traveling around Monterrey in SUVs have committed multiple murders almost every day in the past week, killing more than two dozen people.

Nuevo Leon and neighboring Tamaulipas state have been rocked by a wave of violence unleashed by drug traffickers battling for control of smuggling routes into the United States.

More than 1,100 people, including about 80 police officers, have died in the violence in Nuevo Leon in the past year.

The violence intensified in the two border states after the appearance in Monterrey in early 2010 of giant banners heralding an alliance of the Gulf, Sinaloa and La Familia drug cartels against Los Zetas.

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 15,270 people died in drug-related violence in Mexico last year, and nearly 40,000 people have died since President Felipe Calderon declared war on the country's cartels shortly after taking office in December 2006.

Calderon has deployed tens of thousands of soldiers and Federal Police officers across the country to combat drug cartels and other criminal organizations.

The anti-drug operation, however, has failed to put a dent in the violence due, according to experts, to drug cartels' ability to buy off the police and even high-ranking officials.