Shop owners shuttered their businesses and demonstrators built up street barricades Saturday after President Vicente Fox ordered federal police to intervene in this picturesque city torn by more than five months of protests and violence.

Fox, who leaves office Dec. 1, had refused repeated earlier requests to use force in Oaxaca even as the city slid toward chaos. But gunbattles Friday that killed a U.S. journalist and two Mexicans apparently exhausted his patience.

It was unclear how many members of the Federal Preventative Police were converging on the city, though officers in gray uniforms and carrying riot shields poured off of several flights arriving at the airport, which was closed to commercial traffic Saturday.

Leftist demonstrators demanding the ouster of Gov. Ulises Ruiz have blockaded streets for months and claim the state government has sent gunmen and thugs to provoke them. On Saturday they fortified their positions, piling sandbags and parking large trucks and buses across roads leading into the center of the city.

Teachers' union leader Daniel Rosas said protesters believe that 4,000 federal police officers had arrived in Oaxaca.

At one radio station occupied by protesters, men were seen removing broadcast equipment, destined for an unknown location. A second station held by leftists remained on the air, urging Oaxaca's residents to beat back federal police.

Few people ventured out of their homes Saturday. Throughout the heart of the city, nearly all shops, restaurants and storefronts closed early. Street vendors packed up their wares and disappeared.

"We're afraid," said Juan Lopez, who was pulling metal shutters down over the glass storefront of a sporting goods shop half a block from Oaxaca's leafy central plaza. "We're afraid there is going to be more shooting."

Friday's shooting began when gunmen tried to remove a street blockade in Santa Lucia del Camino, a working class community on Oaxaca's outskirts. Journalist Bradley Roland Will, 36, of New York City, was shot in the abdomen and died later at a Red Cross hospital.

Will worked for Indymedia.org, an independent Web-based organization, and also sold video footage on a freelance basis.

Oaxaca Attorney General Lizbeth Cana, who has likened the protesters to urban guerrillas, said the shooting was sparked by angry residents defending themselves.

"The people are fed up with permanent violence, threats and kidnappings," she said.

But U.S. Ambassador to Mexico Tony Garza said in a statement that the shooters may have been police, and Mexico City newspaper El Universal on Saturday published photos identifying some of the men firing at protesters as local officials.

Santa Lucia del Camino Mayor Manuel Martinez Feria said five men who appeared in the photos brandishing pistols had been turned over to state authorities for possible involvement in Will's killing. He identified them as two members of the local city council, two municipal police officers and the former justice of the peace of a nearby town.

A photographer for Mexican daily newspaper Milenio was also slightly injured in the shootout.

U.S. consular agent in Oaxaca Mark Leyes said American officials were demanding that those responsible be punished.

Will's body remained in a morgue alongside the Red Cross hospital where he died, awaiting instructions from relatives.

Oaxaca resident Esteban Zurrita was also shot dead Friday and the bullet-ridden body of another man, Emilio Alonso Fabian, was discovered about two miles away. Several other shootouts erupted and Red Cross officials they treated 18 other victims, though none suffered gunshot wounds.

What began as a teacher's strike in May has become a continuing battle for control of Oaxaca's streets as protesters have occupied the central plaza for five months, building barricades, seizing radio and television stations, driving out police and burning buses.

Teachers began protesting for higher pay and better working conditions, but after police attacked one of their demonstrations in June, they extended their demands to include a call for the resignation of Ruiz and were joined by leftists, students and Indian groups.

The protesters accuse the governor of rigging the 2004 election to win office. Friday's clashes came a day after teachers agreed to end their strike that has kept 1.3 million children out of classes across the state — a move that had been expected to take the sting out of the protests. But Rosas said late Saturday that Fox's decision to send federal forces could negate Thursday's agreement.

Police — often in plain clothes — and armed gangs have led sporadic attacks on the protesters, and at least five other people have been killed. The lawlessness has led to armed groups of protesters and other residents patrolling the street, frequently capturing and beating suspected criminals.

Ruiz repeatedly asked federal authorities to send troops to restore order, but Fox's government had insisted on trying to solve the dispute through negotiations.