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.
The explosives underscore concerns that drug lords may turn to bombings. E-mails and other intercepted communication indicate that the cartels are seeking explosives for attacks, possibly on buildings or along roadsides, according to a federal intelligence official who spoke on condition of anonymity because he was not authorized to release sensitive information.
In February, assailants stole a tractor-trailer carrying 18 tons of industrial explosives in the northern state of Coahuila, although it was later abandoned on the side of a road as federal police hunted for it.
"The explosives that they have seized have been relatively crude and unsophisticated," Posey said. "But as with any bomb maker there is going to be a learning curve. The fact that we are starting to see (explosives) pop up and becoming more visible is definitely concerning."
Brig. Gen. Edgar Luis Villegas said the cartels' increasingly aggressive tactics are "desperate reactions by criminal gangs to the progress made by federal authorities."
The government has arrested several top drug lords and their lieutenants since President Felipe Calderon deployed troops and federal police across the country more than three years ago to wrest territory from the cartels.
The human cost has been high: Drug-related violence in Mexico has claimed 17,900 lives. Killings of police and journalists are common, and gang members have resorted to especially brutal tactics such as decapitations and killing their enemies' relatives in hopes of intimidating any who would oppose them.
The cartels have been battling not only authorities but each other, competing for turf and drug routes. Much of the current violence centers on a split between the powerful Gulf cartel and its former allies, the Zetas.
The Gulf cartel has apparently formed an alliance with other cartels seeking to exterminate the Zetas. Through banners and e-mails, it has warned residents not to leave their homes, saying the conflict will get worse.
"With the crime, we can't do anything. We have a lot of fear of a stray bullet," said a woman who sells roast chicken from her dirt-floor home next the main army base in Reynosa.
The woman, too terrified to give her name two days after gunmen blockaded the base, said her children are forbidden to leave the house except for school. She won't let her 13-year-old daughter return to her job bagging groceries, even though the family desperate needs the money.
"When the children go to school, I'm scared that they're not going to come back," she said. "I want to go to church to pray for help but I can't leave."
Gunmen kept up the fight Thursday, blockading roads again in Reynosa. One attacker was killed in a shootout between soldiers and armed men in the city's main Hidalgo Boulevard, according to the state government. Farther south in the port city of Tampico, gunmen ambushed a state police checkpoint, killing a commanding officer and wounding another policeman and bystander.
Mexican cities near the eastern end of the U.S. border had until recently been calm while drug violence claimed thousands of lives to the west. That started changing recently with the breakup of the Zetas-Gulf alliance.
The feud escalated when a member of the Zetas was killed in Reynosa in January, perhaps because he was in the Gulf cartel's territory without properly announcing himself. Battles ensued when the Gulf cartel refused to hand over the man responsible to the Zetas, U.S. officials have said.
Olson reported from Mexico City. Associated Press Writer Mark Stevenson in Mexico City contributed to this report.