Human rights activists in Mexico are warning of possible renewed violence in the troubled southern state of Chiapas, which was the scene of a brief, but bloody uprising in January 1994.

The International Civil Oversight Commission on Human Rights is calling for continued focus on Chiapas because of fears of more violence in the impoverished southern state. Activists say visits to rural areas in Chiapas earlier this year produced clear signs of unrest that could lead to violent clashes.

The human rights advocates are calling on both the federal and state governments to take steps to address the root causes of the conflict, and to promote peace.

On Sunday, gunmen in rural areas of Chiapas killed three leaders of groups associated with the Zapatista National Liberation Front. The so-called Zapatistas launched a rebellion in Chiapas in 1994 that led to scores of deaths. Attempts to resolve the conflict peacefully have failed, although a cease-fire has been in place there for more than seven years.

Last year, Zapatista leader Subcomandante Marcos led a caravan of several hundred supporters up to Mexico City from Chiapas, and addressed a huge crowd in the city's main square. Since that time, however, little has been heard from the colorful, masked guerilla leader, whose real name is Rafael Guillen. He was a leftist college professor, before he entered the jungles of Chiapas in the mid-1990s to organize a rebellion there among the poor indigenous people.

Chief government negotiator for Chiapas Luis H. Alvarez says he believes Subcomandante Marcos may be ill. Others have speculated that the rebel leader may have slipped out of his jungle hideout, and may have even traveled abroad. In years past, the Zapatista leader would issue long communiques to news organizations, and also place them on the rebel Web site, but he has been silent now for more than a year.