Leftist protesters trying to force out the Oaxaca state governor set fire to another building Sunday after a night of torching government offices and vehicles in running street battles with police that injured at least 43 people.

The violence broke out late Saturday after masked youths broke away from a protest march by about 4,000 people and began attacking police and buildings in picturesque Oaxaca city.

Youths hurled rocks, fireworks and gasoline bombs in a failed attempt to encircle federal police holding the main square, which security forces took back in late October from protesters who had held it for months demanding Gov. Ulises Ruiz resign for alleged corruption.

Police drove off the attackers with tear gas and jets of water from tanker trucks, then advanced in massed ranks to drive protesters from a camp at a smaller plaza two blocks away.

But bands of young people rampaged through downtown, pushing shopping carts filled with rocks and gasoline bombs.

Court offices in one of Oaxaca's imposing colonial buildings were gutted by flames, and the gangs burned 20 private vehicles and attacked three hotels, throwing gasoline bombs at one and smashing windows at two.

Fires also damaged four buildings housing government offices, one university building and the state hotel association, which has seen tourism reduced to a trickle by six months of demonstrations and violence. Some of the youthful protesters looted several shops.

Firefighters quelled the blazes by early Sunday, but later in the day protesters set a tax office on fire.

Downtown residents watched in horror as buildings burned and streets filled with choking clouds of tear gas and smoke.

Oaxaca resident Josefina Quiros said protesters loosely organized under the leftist People's Assembly of Oaxaca were spreading fear. "We are terrified of the APPO people," she said, referring to the movement by its Spanish initials.

In a press statement, the federal police said 152 people had been arrested and accused outside activists of participating in the unrest, which it said resulted in injuries to four officers and an unspecified number of bystanders.

The statement also said federal police would no longer stay mainly at posts in the main square and a few other spots around the city, but would actively patrol in search of those responsible for "direct attacks on federal police."

State prosecutors said at least 43 people were injured. It was unclear whether that figure included police officers and three journalists who suffered minor injuries during the confrontations.

Prosecutors said there were no reports of deaths. Marcelino Coache, a spokesman for the anti-Ruiz movement, said some protesters suffered serious injuries.

Making one of his first visits downtown since protesters forced state officials out in May, Oaxaca's governor viewed the damage and vowed to punish those responsible.

"All the weight of the law will be applied to those who have committed these acts of vandalism," Ruiz told reporters.

Ruiz earlier blamed the disturbance on radical groups from Mexico City. "These are the death throes of a movement that has already disintegrated," he said at a news conference.

The unrest began as a strike by teachers, but mushroomed into a broad protest against social and economic injustices in this poor state. Protesters focused their anger on Ruiz, accusing him of brutality, corruption and electoral fraud.

A majority of teachers have returned to work and did not participate in Saturday night's demonstration.

Nine people have been killed over the months, including freelance video journalist Bradley Roland Will, 36, of New York, who was filming a group of leftist protesters clashing with a group of armed men. Guns were fired by both sides, although it was not clear who shot first.