Marcos has never confirmed that he is who the government says he is: Rafael Sebastián Guillén, son of furniture seller Alfonso Guillén Guillén, of the city of Tampico, in the northern state of Tamaulipas.

The Zapatistas, based in the jungles of the southern state of Chiapas, did not respond immediately to requests for comment Monday night after reports of Alfonso Guillen's death appeared on newspaper Web sites and Mexican radio stations. The reports said Guillen's funeral was scheduled for Tuesday morning in Tampico.

CONDOLENCES

Luis H. Álvarez, President Vicente Fox's special envoy to the Zapatistas, offered his condolences to Marcos in a letter that the government later distributed to national and foreign news media.

"If you are not Rafael Sebastián ... I beg you to not take offense to these lines I write to you today, in a gesture of sorrow and in memory of a good man," Álvarez wrote.

Marcos has been at the public forefront of the Zapatista movement since rebels burst from the jungles of the southern Mexican state of Chiapas on Jan. 1, 1994, to occupy several cities in the name of Indian rights and equality The rebels quickly settled into a tense cease-fire with the government. Since then their movement has been largely nonviolent.

In 1995, the federal government officially identified Marcos as Guillén, a former university instructor.

In an interview following the government's announcement, Alfonso Guillén said Marcos had all of the physical and intellectual characteristics of his son.

The Reforma newspaper reported that Guillén was 85 at the time of his death. El Universal said he was 81.