Mexico's president said Thursday the army will continue to battle the country's drug cartels, despite recent protests asking for the soldiers' withdrawal.

Hundreds of people blocked bridges to the United States in three border cities Tuesday, demanding the army leave and accusing soldiers of abuse. Both state and federal officials have alleged the protests are organized by drug gangs, noting that some of the protesters masked their faces.

In an Army Day speech in the northern city of Monterrey, President Felipe Calderon defended his decision to send some 45,000 troops nationwide to take on the drug gangs. He also called on all Mexicans to "stand behind our army's fight against this common enemy."

"When we've recovered the rule of law in areas vulnerable to organized crime, and local authorities are capable of fighting this scourge, then the army will have completed its mission," he said.

Calderon vowed "to continue fighting organized crime, without pause or mercy."

Human rights activists have accused soldiers of numerous abuses during anti-drug operations, including cases in which patrols allegedly shot and wounded civilians at military checkpoints and illegally jailed and tortured people during raids aimed at traffickers.

While Calderon's government has acknowledged some cases of army abuse, officials claim the problems have been isolated.

Calderon said Thursday that 78 soldiers have been killed in the past two years in the battle against drug cartels. Last year, more than 6,000 people lost their lives to organized crime as the powerful, well-funded cartels fought each other for territory and battled the army offensive.

The growing violence has forced some Mexicans to question the army crackdown. But Calderon says Mexico has no choice but to fight.

"Mexico faces a historic challenge in converting itself into a safe country, a country of true law and order," he said.

In the northern state of Chihuahua, gunmen shot to death a member of the town council in Guadalupe, just southeast of the border city of Ciudad Juarez. She was the second councilwoman killed this week in Guadalupe, a town where drug gangs have been active.

Patricia Guadalupe Avila was shot to death in her vehicle Thursday, just four days after fellow councilwoman Cristina Aranda was shot and died in Guadalupe, state prosecutors said.