Security officials in the northeast Mexico state of Tamaulipas say they have killed four gunmen in a town near the U.S. border.

The Tamaulipas Coordination Group says in a statement Thursday that a military patrol in Ciudad Mier came under attack early Tuesday from a four-vehicle convoy.

It says the soldiers fired back and killed three men and one woman. The statement says the dead have not been identified and were wearing camouflage, helmets and military-style boots.

For several years Ciudad Mier has sat at the center of territory fought over by the Gulf and the Zetas cartels. In late 2010, the battle for the town grew so intense that most of its 6,000 residents fled with some seeking refuge at a shelter in neighboring Miguel Aleman.