Another front beckons.

Mexican drug traffickers have escalated their arms race, acquiring military-grade weapons, including hand grenades, grenade launchers, armor-piercing munitions and antitank rockets with firepower far beyond the assault rifles and pistols that have dominated their arsenals.

The proliferation of heavier armaments points to a menacing new stage in the Mexican government's 2-year-old war against drug organizations, which are evolving into a more militarized force prepared to take on Mexican army troops, deployed by the thousands, as well as to attack each other.

At least one grenade attack north of the border, at a Texas nightclub frequented by US police officers, has been tied to Mexican traffickers.

"At this stage, the drug cartels are using basic infantry weaponry to counter government forces," a US government official in Mexico said. "Encountering criminals with this kind of weaponry is a horse of a different color," the official said.

"It's not your typical patrol stop, where someone pulls a gun. This has all the makings of an infantry squad, or guerrilla fighting."