Protesters vowed to re-establish street blockades in embattled Oaxaca City after forcing Mexican federal police to retreat at a key intersection following more than six hours of clashes involving tear gas and gasoline bombs.

Thursday's battle left 20 protesters, 10 police and three news photographers injured, after youths wearing bandannas over their face lobbed rocks, large bottle rockets and gasoline bombs at police, who responded with tear gas, water cannons and the rocks pitched at them.

The clash occurred near the state university, where protesters demanding the ouster of the state's governor have set up headquarters and broadcast from a radio station after police retook the city's picturesque central plaza during a massive raid Sunday. Police control in other areas of the city has since been spotty.

Reverberations from the ongoing fight in Oaxaca city — seized five months ago by a coalition of striking teachers and leftist protesters demanding the resignation of the Oaxaca state governor — also reached the capital of Mexico City, where sympathizers temporarily blocked some downtown streets to demand police be withdrawn from Oaxaca.

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In Oaxaca City, about 200 police wearing body armor and carrying riot shields advanced to the university gates and fought the protesters for more than six hours before retreating. The retreat left protesters claiming victory and pledging to re-establish barricades that had been dismantled in previous days.

Under Mexican law, the university rector must give the police permission to enter. Rector Francisco Martinez, speaking on the university radio station, called the operation an "attack" and demanded that the police withdraw.

Federal police said they simply intended to "restore order and peace" on the streets and didn't plan to storm the school.

Previous negotiations between the protesters and the interior department broke down, and on Thursday protest spokesman Florentino Lopez demanded direct talks with President Vicente Fox.

A free medical clinic near the university reported that more than 20 protesters had been treated for bruises, cuts and injuries related to tear gas. Lopez claimed the number of injured was much higher.

The 10 officers received various gas-fire burns and bruises, the federal police said in a statement.

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Photographer David Jaramillo of the Mexican daily El Universal was hit in the arm by a large bottle rocket loaded with nails, and was hospitalized in stable condition, the statement said. Another two photographers suffered minor injuries after being hit by stones or nails packed in the rockets, which are about an inch in diameter and six inches (15 centimeters) long.

The university radio station reported that at least six demonstrators had been arrested and demanded their release.

The university is a stronghold of the movement to oust Oaxaca Gov. Ulises Ruiz, who is accused of rigging the 2004 election to win office and organizing bands of thugs to attack dissidents. Protesters including trade unionists, leftists and Indian groups have been flocking to Oaxaca since May to press their demands, and took over the center of the state capital for more than five months.

Many of the protesters retreated into the university campus on Sunday after thousands of federal police swept into Oaxaca center firing tear gas and tearing down camps and barricades. It was unclear exactly how many remained there.

At least nine people have died in the conflict, mostly protesters shot by police or armed gangs. Among the victims was activist-journalist Bradley Roland Will, 36, of New York, who was shot in the stomach while filming a gunbattle Friday.

The state prosecutor's office said Wednesday that two people were in custody in connection with Will's death. They were detained after residents identified them as the alleged shooters, and Mayor Manuel Martinez of Santa Lucia del Camino, where Will was killed, said the suspects are officials of the municipality, on the outskirts of Oaxaca City. The embassies of the U.S., Canada, Britain, France and Germany all have warned their citizens to avoid traveling to the region.

The conflict has shattered tourism in the city, which is popular for its colonial architecture and ancient ruins.