Both men say they only confessed after being tortured for several days and claim they were being punished for their attempts to defend the forests of the Sierra Madre mountain range from rapacious logging.

They were backed by international human rights groups and have been awarded a number of prestigious human rights and environmental awards.

Fox had been under intense pressure from rights groups to take action in their case, and his move yesterday immediately freed the two from prison in Iguala, Guerrero.

Fox said he had taken into account requests for their freedom, their medical condition and a report from a U.N. working group on arbitrary arrests.

"With these actions we demonstrate through deeds my government's commitment to the promotion and observance of human rights in our country," Fox said at a news conference, adding that their release was in line with international conventions on human rights and torture.

The case returned to the national spotlight last month when one of Mexico's most prominent human rights lawyers, Digna Ochoa, was shot dead in her office.

Ochoa had represented Montiel and Cabrera, and officials believe her murder was linked to the ongoing disputes between environmentalists and logging interests in Guerrero.

"The lines of inquiry are pointing toward the state of Guerrero, toward the conflicts of the peasant farmers with logging groups," Mexico City Prosecutor Bernardo Batiz said earlier this week.

Mexico's state news agency Notimex quoted Mariclaire Acosta, the government's top human rights official, as saying Montiel and Cabrera were released on humanitarian grounds because they both suffered from poor health.

Montiel was imprisoned for seven years on charges that he cultivated marijuana and was in possession of weapons, while Cabrera received a 10-year sentence on gun charges.