Armed with assault rifles, grenades, homemade explosives, and bulletproof vehicles, scores of gunmen attacked two army garrisons in northern Mexico in a series of seven simultaneous attacks, the Associated Press reports. In at least three instances, gunmen tried to blockade soldiers inside their bases. In the ensuing firefights, 18 of the fighters died. While drug gunmen often shoot at patrolling soldiers, it's unusual for them to mount such a forceful attack on army bases. In recent months, drug-related bloodshed has spiked in the border states of Tamaulipas and Nuevo Leon as the Gulf cartel formed an alliance with other cartels against its former allies, the Zetas gang. Gen. Edgar Luis Villegas called the attacks "desperate reactions by criminal gangs to the progress being made by federal authorities" against drug cartels.