Updated

Federal forces detained 10 mayors and 18 other officials Tuesday for allegedly protecting one of Mexico's most violent drug cartels in an unprecedented anti-corruption sweep in the Pacific coast state of Michoacan.

Soldiers and federal agents fanned out across President Felipe Calderon's native state to carry out the operation, which an expert called a blow to the political class tied to traffickers in Michoacan.

The officials, who had been under investigation for six months, allegedly leaked sensitive information and provided protection to La Familia cartel, said Ricardo Najera, a spokesman for the federal Attorney General's Office. He declined to give more details to avoid compromising the case.

More than 200 federal agents burst into the state attorney general's office in Morelia to detain three of the officials.

Most of the mayors were from towns in a mountainous region where there have been numerous beheadings and federal agents recently found 22 methamphetamine laboratories. Among those detained was the mayor of Uruapan, where La Familia gunmen dumped five human heads on a bar dance floor in 2006, the Attorney General's Office said in a statement.

The mayors came from different parties, including Calderon's own conservative National Action Party.

The detentions of elected officials show how Mexican cartels have infiltrated the country's political structure and how far-reaching their control is in rural Mexico, said Victor Clark, an expert on trafficking based in the drug-plagued northern border city of Tijuana.

It also marks a first for the federal government, which has arrested scores of corrupt police officers in the past but has never gone after such a large group of mayors.

"This is a huge blow to the cartel. These ties are indispensable for the operation of these organizations," said Clark, director of the Binational Center for Human Rights in Tijuana. "But until now the government has never dared to touch the political classes tied to drug trafficking. For me this is an important step."

High-ranking state police officials and two municipal police chiefs were among those detained Tuesday, including state police academy director Mario Bautista and the state governor's adviser, Citlalli Fernandez, who also is the former public safety secretary, the Attorney General's Office said.

Meanwhile, the federal Public Safety Department paraded before the news media 11 suspected La Familia members who were detained late Monday and early Tuesday in the states of Michoacan and Mexico, among them a former Michoacan state police officer.

Najera declined to say whether those arrests were related to the Michoacan operation.

The sweep drives home Mexico's struggle to weed out corruption in its drug fight. Many local and federal police have been arrested on charges of protecting drug cartels since Calderon launched his nationwide crackdown on organized crime in 2006. More than 10,750 people have died in drug violence since the crackdown started.