Mexico ? In a ratcheting up of tactics in a long, bloody war, drug cartel gunmen made seven especially brazen assaults on Mexican soldiers in one day this week, throwing up roadblocks near army garrisons and spraying checkpoints with automatic weapons fire.

The apparently coordinated assaults raise the prospect that parts of Mexico could be descending into open warfare between the cartels and the government.

Drug bosses appeared to have little to show for Tuesday’s attacks near the Texas border except a body count for their own side: 18 attackers dead, while the military said its own casualties were limited to one soldier with a wounded toe.

But there have been more attacks since, and the battles have shown that gang henchmen are as well armed, if not as well trained, as the soldiers. Armored vehicles, explosive devices and grenade launchers were among the items the military seized.