The Mexican government's peace negotiator for Chiapas called on the leftist Zapatista rebels to lay down their arms and stop supporting violent causes.
The public call, issued on Wednesday by negotiator Luis Alvarez, accused rebel leader Subcomandante Marcos of being "incongruous" by supporting last week's violent street clash with police in central Mexico, and suggested that former rebel supporters were leaving the ranks of the movement in the southern state of Chiapas.
"The Zapatista National Liberation Army has an obligation to hand over their weapons, and leave behind the deplorable threat of violence they represent," Alvarez wrote in an open letter to the rebels.
In one of the harshest criticism he has made of the rebel leader, Alvarez wrote that "Marcos is being incongruous by taking up causes that have expressed themselves violently ... putting aside the interests of the Indians he claims to represent."
Alvarez -- whose invitations to sit down and talk with Marcos have long been rebuffed by the rebel leader -- also suggested the Zapatistas were losing support in Chiapas, where the rebels held a brief armed uprising in January 1994 to demand greater Indian rights.
"In contrast with the attitude of the Zapatista leadership, several communities that were identified with them have changed their way of thinking," the letter said.
That appeared to be a reference to the fact that, while the Zapatistas reject all government aid, people in some towns allied with them are starting to accept it.
The rebels have been allowed to retain their weapons -- not believed to number more than a few hundred -- under an uneasy truce.
On Tuesday, Marcos gave a rare television interview in which he defended protesters in the town of San Salvador Atenco who were seen last week on television footage battle police with rocks, machetes and gasoline bombs, and beating an unconscious policeman.
Marcos said the attack against the police stemmed from "people's furor," and claimed "they were not beating the person, but rather what he represents."
The protests started after police tried to relocate street vendors.
Marcos holds rally
But after police retook the town -- and beat some protesters -- Marcos showed up to hold a rally and pledged to hold demonstrations demanding the release of those arrested in the clash.
Marcos also denied accusations by presidential candidate Roberto Madrazo that the Zapatistas instigated last week's riot in San Salvador Atenco, about 25km northeast of Mexico City.
The violent clashes between residents and police left one dead and dozens injured.
The rebel leader came out of his jungle hide-out in January and is on a quixotic, one-man tour of Mexico trying to forge a national leftist movement.
Marcos -- identified by Mexican authorities in 1995 as former university instructor Rafael Sebastian Guillen -- enjoyed almost rock-star popularity among many Mexicans following the Zapatistas' uprising.
But since January his talks and tour appearances have not drawn large crowds, leading some to suggest he is trying to capitalize on the street violence to revive his flagging movement.