After trying for more than four years to bring a peaceful solution to the conflict in southern Mexico, a group of mediators led by the Roman Catholic church has decided to step down.

They criticised 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.