Organized crime gangs have killed at least 13 people over the past four days in attacks on taxi drivers and buses in the Mexican resort city of Acapulco, officials in the Pacific coast state of Guerrero said.

Armed assailants allegedly targeted the taxi and bus drivers because they suspected them of collaborating with rival gangs, that state's Public Safety Secretariat said on its Web site.

It added that four taxi drivers were killed Thursday morning at a taxi stand near Acapulco's municipal market, an attack that also left two other people wounded.

In previous days, gunfire attacks targeting at least four urban buses on different roads and avenues left seven people dead.

On Monday and Wednesday, another two taxi drivers were killed in different parts of Acapulco. Although authorities said the motive for the crimes is unclear, they have not ruled out the possibility of a settling of scores among organized criminals.

A source with the Guerrero state Attorney General's Office told Efe the attacks on taxi and public transport drivers have occurred because "organized crime gangs identify them as informants for the cartel that operates in this city."

Authorities say the Cartel Independiente de Acapulco - a splinter group of the Beltran Leyva cartel and a gang led by Edgar Valdez Villarreal, who was known as "La Barbie" and was arrested by the federal police on Aug. 30, 2010 - is active in the port city.

They say this gang, which has been battling a rival known as the Comando del Diablo for control of the illegal drug trade in Acapulco, is responsible for dozens of murders and maintains networks of informants among public transport drivers.

The gang war has been marked by shootouts in the streets and the discovery of mutilated bodies with "narco-messages" in Acapulco and other parts of Guerrero.

Tourism industry leaders say the wave of drug-related violence is partially to blame for a drop in the number of visitors to the resort city.

Elsewhere, 10 suspected organized crime gunmen were killed in a clash Thursday with army soldiers in the northeastern town of Agualeguas, military officials said.

An official with the 7th Military Zone said the soldiers came under fire while inspecting a house in that town, located in Nuevo Leon state, and a shootout ensued.

Following the gun battle, the soldiers seized 11 weapons, ammunition clips, ammunition, fragmentation grenades, drugs and vehicles.

Nuevo Leon has been the scene of a turf war dating back to 2010. More than 1,100 people have been killed in the fighting between the Gulf cartel and its former allies Los Zetas for control of that state, a strategic drug-smuggling corridor.

In other gangland violence, the bodies of four men and five women bearing signs of torture were found in the northern state of Chihuahua, officials said Thursday.

Six of the corpses were found in Ciudad Juarez, a violent border city across from El Paso, Texas, and three others in the state capital of Chihuahua.

Chihuahua is one of the Mexican states hardest hit by turf battles for control of smuggling routes to the United States, the world's biggest market for illegal drugs.

That state has accounted for almost 30 percent of the more than 40,000 people killed since December 2006 in drug-related violence, which has mostly involved turf battles among the cartels and clashes between the gangs and security forces.

President Felipe Calderon took office that month and gave federal police and the army the lead role in battling the cartels, but the deployment of tens of thousands of federal forces to drug-war hotspots has not stanched the violence.

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