A letter purportedly signed by La Familia drug cartel announcing a one-month truce circulated Sunday in the western state of Michoacan.

In the one-page message, distributed by e-mail and in some cities door by door, the gang claims it will halt all crime activity during January to demonstrate that the cartel "is not responsible for the criminal acts federal authorities are reporting to the media."

Prosecutors have not verified the letter's authenticity, according to an employee of the Michoacan bureau of the federal Attorney General's Office who spoke on condition of anonymity because he is not authorized to discuss the matter publicly.

The government says La Familia has been weakened by a recent string of arrests and deaths of top leaders.

In another letter that circulated in November, La Familia purportedly offered to disband.

Last month, gunmen torched vehicles across Michoacan and used them as barricades to block all entrances into the state capital of Morelia after federal police killed alleged La Familia leader Nazario Moreno Gonzalez.

La Familia has occasionally made public pronouncements seeking to convince the public that it is defending Michoacan against other drug gangs.

Federal officials, however, say the cartel has terrorized the state with kidnappings, extortion, hundreds of murders, decapitations and drug trafficking.

More than 30,000 people have died in drug-related violence nationwide since President Felipe Calderon launched a crackdown on cartels after taking office in December 2006, first deploying hundreds of soldiers and federal police to his home state of Michoacan.

On Sunday, Calderon said in a New Year's broadcast that his administration will continue to fight organized crime.

"We all know it is necessary to rid Mexico of crime, impunity and corruption, which had been rooted in our society and our institutions," he said. "I can assure you we are on the right path and we will defeat the criminals, to ultimately build a Mexico of peace."

Earlier Sunday, military and federal agencies responsible for fighting the drug war released a joint statement highlighting what they called "historic achievements."

In Calderon's first four years in government, more methamphetamine, automatic rifles and grenades were seized than in the previous eight years, the statement said.

It did not say how seizures for cocaine and marijuana, the main sources of income for Mexican drug cartels, compare to previous administrations.

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Associated Press writer Olga R. Rodriguez contributed to this story from Mexico City.