The group of mediators, led by the Roman Catholic church, has decided to step down, criticising the government's military campaign in Chiapas state and its refusal to meet the demands of left-wing Zapatista rebels.

The leader of the commission, Bishop Samuel Ruiz, said the government had chosen a strategy in which the mediators could play no part. He also condemned what he called government aggression against the church - saying priests had been arrested and churches defiled by security forces.

The situation of the indigenous people of Chiapas has fuelled the Zapatista rebellion

The commission has been seeking a solution to the conflict for four years, but it is now more than a year since the two sides last met. The BBC Mexico correspondent says the mediating commission's demise is the clearest sign so far that the peace process is now in total disarray.

In a written statement, the commission criticised the government's military campaign in Chiapas and its refusal to meet rebel demands.

The mediating commission's decision to disband closely followed the resignation of Bishop Ruiz from his position as chair. In a Sunday homily to his parishoners, the bishop said he no longer felt able to mediate between the government and the Zapatistas, who took up arms in 1994.