The operation is the first major offensive against drug gangs by President Felipe Calderón, who was sworn in on Dec. 1 after narrowly winning election on a law-and-order platform.

"We are looking to take back the spaces that organized crime has seized," said Interior Secretary Francisco Ramírez Acuña, flanked by the attorney general and heads of the army, navy and federal police. "The battle against organized crime has just begun."

Michoacán, Calderón´s home state, has had more than 500 killings this year, about half of which investigators say are linked to a turf war between two rival drug gangs.

In apparent attempts to terrorize those that oppose them, the gangs have carried out a wave of decapitations, placing the severed heads on public display with threatening notes including one that read, "See. Hear. Shut Up. If you want to stay alive."

In the most gruesome case, gunmen burst into a nightclub and rolled five heads onto the dance floor. In another, a pair of heads were planted in front of a car dealership in Zitacuaro, a town best known until now as a nesting ground for monarch butterflies.

Security officials said police and soldiers will arrest drug traffickers, mount checkpoints and burn crops of marijuana and opium poppies grown in Michoacán´s rugged mountains.

Naval ships also will seal off the state´s small Pacific coast, along which smugglers carry drugs on their way north to the United States.

Officials also announced they had made a wave of major drug busts in other states since Calderón took office two weeks ago, seizing more than two tons of cocaine and nearly 20 tons of pseudoephedrine, used to make methamphetamine.

Calderón, a career politician from the conservative National Action Party (PAN), has vowed to smash the drug gangs who have become a grave problem for the nation´s security forces.

Across Mexico, there have been more than 2,000 drug-related killings this year, including several police chiefs, journalists, town mayors and at least one judge.

Many security experts say it will take more than just brute force to defeat the cartels, who are heavily armed, using rocket-propelled grenades and bazookas, and well financed, making billions of dollars smuggling marijuana, heroin, methamphetamine and cocaine into the United States.

Calderón´s predecessor Vicente Fox promised the "mother of all battles" against organized crime, sending in thousands of soldiers and federal police to some drug embattled towns and arresting several major drug kingpins.

But the arrests appeared to spark more violence as up-and-coming gangsters battled to take over the smuggling routes of those who were killed or arrested.

Federal investigators say the violence in Michoacán stems from a turf war between a local gang called Los Valencia and the northern Mexico Gulf cartel, whose bloody enforcers are know as the Zetas, a group of ex-Mexican army operatives turned hit men.

The killings rose in 2004 following the arrest of Valencia leader Armando Valencia and his lieutenant Carlos Alberto Rosales Mendoza. Investigators say their arrests encouraged Gulf Cartel leaders to try to battle their way into their territory.