Thirteen people died in three shootouts involving marines and gunmen in Tamaulipas, a state in northeastern Mexico, state officials said.
"None of the victims have been identified," the Tamaulipas Coordination Group said in a statement.
The shootouts occurred between noon and 4:20 p.m. on Sunday and all of the dead are presumed to be gunmen, officials said.
"The first shootout occurred shortly after midday at kilometer 12 of the Matamoros-Reynosa highway in the community of Esperanza, where armed civilians clashed," leaving "four men and a woman" dead, the Tamaulipas Coordination Group said.
Two SUVs, three rifles, an automatic pistol, ammunition and tactical gear were found at the scene of the shootout, the Tamaulipas state government said.
The second gunfight happened around 4:05 p.m. at kilometer 2 of the Matamoros-Reynosa highway at a place called La Joroba, state officials said.
The shootout started "as a result of a chase by Marine Corps members of armed civilians traveling in several units" and ended with the deaths of four gunmen at the hands of marines, the Tamaulipas state government said.
Marines found three rifles, ammunition, bullet-proof vests and other gear inside the late-model SUV in which the gunmen died.
The last shootout occurred around 4:20 p.m. on Avenida El Niño in Matamoros, located across the border from Brownsville, Texas, when marines ordered a group of armed civilians to halt.
The marines "were attacked and repelled the aggression," leaving four men dead inside the vehicle they were traveling in, the Tamaulipas state government said.
The shootouts were reported on social-networking sites during the day, but officials did not confirm the incidents until Sunday night.
The Gulf, Los Zetas and Sinaloa drug cartels have been fighting for control of Tamaulipas and smuggling routes into the United States for years. EFE