Reynosa, 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.

The attacks are occurring as two cartels are engaged in a violent power struggle of their own. Experts on the drug war say drug lords are trying to get military patrols out of the way of the gangs' increasingly bloody battle for trafficking routes in the northern border states of Nuevo Leon and Tamaulipas.

"There does seem to be a shift in what's permissible to the cartels. The army used to be off limits," said Andrew Selee, director of the Mexico Institute at the Woodrow Wilson Center. "There is an escalation in what the drug trafficking organizations are willing to do, but it's hard to tell if it's a permanent change in strategy."

The battles climaxed Tuesday with seven assaults against army positions that left 18 attackers dead across Nuevo Leon and Tamaulipas.

The first came when gunmen ambushed soldiers on patrol between Matamoros and the border city of Reynosa, across from McAllen, Texas. An hour later, cartel gunmen used trucks and cars to blockade a garrison in Matamoros and the main army base in Reynosa.

Troops were ambushed six more times throughout the region, including once in Reynosa when soldiers rushed to check reports of another blockade near the offices of Mexico's state oil company. In each of the two deadliest battles, five gunmen were killed.

"What we saw ... over the past couple of days is definitely an escalation in tactics," said Alex Posey, a tactical analyst at Stratfor, a global intelligence company in Austin, Texas.

"When they have engaged the military patrols (previously), it's been a shoot-and-run scenario. Maybe they throw a hand grenade and use small arms fire," Posey said.

The battles indicate that at present, cartels are no real match for Mexico's army - even when soldiers can't call reinforcements from nearby army bases.

"This proves that (soldiers) are tactically superior to the cartel henchmen," Posey said. Soldiers "were able to defeat pretty decisively an ambush on their locations. It actually appears like it was a botched operation from the cartels."

The cartels, however, do match Mexico's military in firepower: Soldiers confiscated more than 50 assault rifles, 61 grenades and eight homemade explosive devices, as well as grenade launchers and six armored vehicles.