Three suspected organized crime gummen were killed and another three were wounded in a clash near the northeastern Mexican city of Matamoros with army troops, who seized more than 100 weapons and nearly a score of vehicles after the gun battle, military sources said.

The Defense Secretariat's 4th Military Region said in a statement that 83 automatic rifles, 18 handguns, five grenade launchers, a rocket launcher, 11 fragmentation grenades, 28 40 mm grenades, 315 ammunition clips, more than 18,000 rounds of ammunition, 17 vehicles and eight kilos of marijuana were confiscated in Wednesday's operation.

The operation began after an air force helicopter detected a convoy of vehicles traveling on a road near Matamoros, Tamaulipas state, and followed them to determine their destination, the secretariat said.

It added that the air force personnel called for army support after gunmen began shooting at the chopper.

When the army troops arrived, the assailants fired gunshots at them and fled in different directions from the soldiers' return fire.

After reinforcements arrived, troops blocked off the area and combed several streets in the zone until they located the abandoned vehicles and weapons.

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

The violence has intensified since the February 2010 appearance in the northern industrial city of 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 nearly 40,000 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.