Thousands of troops rolled into a key Mexican drug stronghold Tuesday to set fire to marijuana and opium fields and round up traffickers, sent by President Felipe Calderon to restore order in a region where smugglers have defied authorities with beheadings and large-scale drug production.

Navy ships were patrolling the Lazaro Cardenas port, a hub for drugs arriving from Central America and Colombia on their way to the United States.

Cornelio Casio, one of several generals overseeing the operation in the western state of Michoacan -- Calderon's home state -- said 6,500 soldiers and federal police were deployed.

"We aren't going to lose any time," he said. "We are completely focused on this war."

The campaign echoes crackdowns by previous Mexican presidents who repeatedly ordered mass firings of drug-corrupted police, revamped courts, sent thousands of troops to battle traffickers and accelerated drug seizures -- without making much of a dent in the quantity of narcotics crossing the U.S.-Mexico border.

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In an interview Tuesday with the Televisa network, Attorney General Eduardo Medina Mora said the operation was aimed at "reconquering territory" controlled by drug gangs.

"It's not just a war against drug lords," he said. "It's a war against the entire criminal structure."

Medina Mora acknowledged drug lords will likely just find another stronghold, saying, "It's a complicated war." But, he added, "It is a war we can win."

Calderon brushed aside concerns the crackdown could lead to violations of human rights and claim innocent victims.

"It's about recovering the calm, day-to-day life of Mexicans who live in the state," he said Tuesday.

Calderon took office Dec. 1, promising to fight the execution-style killings, corrupt police and defiant gangs that plagued Vicente Fox's presidency. Calderon has budgeted more funds for law enforcement and appointed a hard-line interior secretary, Francisco Ramirez Acuna.

U.S. Ambassador Tony Garza has repeatedly expressed concern about the rising violence, some of which has spilled into the United States, and the State Department has warned U.S. citizens about travel to Mexico.

Warring cartels have killed at least 2,000 people this year and forced Fox to send troops into the border city of Nuevo Laredo and the beach resort of Acapulco.

But those efforts failed to deter traffickers, who have left human heads outside government offices accompanied by written warnings. One recent message in Michoacan read: "See. Hear. Shut up. If you want to stay alive."

In the most gruesome case, gunmen burst into a Michoacan nightclub and rolled five human heads onto a dance floor, smearing the white-tile floor with blood. In another, a pair of heads were planted in front of a car dealership in Zitacuaro, a town known as a nesting ground for monarch butterflies.

During his six-year term, Fox arrested several drug lords, creating an underworld power vacuum in the country that is the conduit for most of the marijuana, heroin, cocaine and methamphetamines in the United States.

Investigators say the Gulf cartel was encouraged to battle its way into Michoacan following the 2004 arrest of Valencia drug gang leader Armando Valencia and his lieutenant Carlos Alberto Rosales Mendoza, who are allied with Joaquin Guzman's Sinaloa cartel.

Michoacan's rugged, remote mountains are perfect for growing opium and marijuana.

Security experts say it will take more than brute force to defeat the cartels, which are making billions of dollars and have arsenals that include rocket-propelled grenades and bazookas.

Thousands of federal police and soldiers, dressed in body armor and armed with automatic rifles, arrived Tuesday.

At one highway checkpoint staffed by more than a dozen federal police, officers frisked passengers and searched vehicles for drugs, weapons and drug leaders.

Across the street at a gas station, 50-year-old Alejandro Arias watched. The owner of a small convenience store, he has had to pay drug lords protection money.

"It's been a terrible year. It's gone from bad to worse," he said. "But you have to have hope. We don't have anything else."

In the capital of Morelia, 22-year-old computer technician Hernan Hijano wasn't as optimistic.

"When the soldiers leave, the problems will continue," he said. "This is just for the cameras."