Protesters calling for the governor's resignation regrouped to plot strategy Friday, a day after holding federal police away from one of their strongholds during six hours of often-violent clashes.

The demonstrators lobbed firecrackers, gasoline bombs and rocks at police who had surrounded the Oaxaca state university Thursday and police responded with tear gas and water cannons in a battle that left 20 protesters, 10 police and three news photographers injured.

Federal police said they simply intended to "restore order and peace" on the streets and didn't plan to storm the school, where the protesters have set up one of their headquarters and are broadcasting from the university radio station.

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

Protest leaders later dismissed any chance of resuming negotiations with the federal Interior Department. Spokesman Florentino Lopez demanded direct talks with President Vicente Fox instead. Fox was in Uruguay on Friday attending the Iberoamerican Summit and his office did not issue a statement.

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Federal 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 Gov. Ulises Ruiz — also reached the capital of Mexico City, where sympathizers temporarily blocked some downtown streets Thursday to demand police be withdrawn from Oaxaca.

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.

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 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's center. 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. 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.