OAXACA, Mexico - A protester was shot dead when assailants fired on a march of about 8,000 people calling for the governor's resignation in a southern Mexican state Thursday, adding to months of political violence driving tourists away from a historic city.

Jose Jimenez, 50, was taken to a hospital with bullet wounds and pronounced dead on arrival, said his wife, Clara Jimenez. She said the gunfire appeared to come from a house that marchers passed in Oaxaca City. After the shooting, protesters set fire to the house, and firefighters extinguished the blaze.

Protesters captured four men whom they believe carried out the shooting, said Daniel Rosas, a spokesman for the leftist Oaxaca People's Assembly, which organized the march.

In recent weeks, the protesters have captured several men accused of attacking demonstrators and have handed to them over to federal investigators.

Rosas accused Gov. Ulises Ruiz of being behind the shooting. Officials in Ruiz's office denied the charge and condemned the killing.

The assembly is demanding Ruiz' resignation, accusing him of using force to repress dissent and of rigging the 2004 election to win office.

On Wednesday, gunmen killed three people, including a 12-year-old boy, on a road about 150 miles from Oaxaca. The three had been heading to protests in the city, but police said they did not know if the attack was linked to the demonstrations.

The mountains of Oaxaca have long been plagued by violence linked to land disputes, drug trafficking and banditry. But Wednesday's killings may have been carried out by another leftist group because of political infighting, said Jorge Albino Ortiz, another spokesman for the People's Assembly.

Tensions in Oaxaca have been on the rise since June, when state police attacked a demonstration of striking teachers occupying the historic central plaza and demanding a wage increase.

Since then, thousands of teachers, unionists and leftists have camped out in the plaza, spray-painting buildings with revolutionary slogans, smashing hotel windows and erecting makeshift barricades. Most businesses remain closed.

The unrest has paralyzed one of Mexico's top cultural attractions, where visitors to the southern city normally browse traditional markets for Indian handicrafts, hike ancient pyramids and stroll cobblestone streets to sample mole dishes.