Masked lawmen clutched automatic rifles on rooftops as more than 20,000 people marched toward police encampments on Sunday yelling "Get out federal police!" sparking fears of more violence in this embattled southern city.

Many of the leftists were armed with clubs, spray paint and fireworks as they poured out of the public university where they had set up their base and headed toward the city center where federal police have been camped for more than a week.

The student radio reported that gunmen had fired at some protesters near the university early Sunday morning, injuring a 21-year old student who was taken to a public hospital.

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About 4,000 federal police swooped into the city on Oct. 29 to restore order following a five-month-old protest that has rattled President Vicente Fox's administration, scared tourists out of Oaxaca and left at least nine people dead, mostly protesters shot by armed gangs.

Protesters are demanding the resignation of Oaxaca Gov. Ulises Ruiz, who they accuse of rigging the 2004 election to win office and sending groups of gun-toting thugs against his opponents.

The demonstrators also want the federal police to leave.

"They don't guarantee security, to the contrary, they scare us and are rude," said Jesus Velasco, 60, a businessman marching Sunday.

Protest leader Flavio Sosa, wanted by state police on conspiracy and riot charges, said the protesters won't look for a fight, but fears police or Ruiz's agents may provoke one.

"Our enemies carry out murders, persecution, and arbitrary arrests," Sosa told The Associated Press on Saturday. "We have the right to defend ourselves."

Archbishop Jose Luis Chavez called for an end to the conflict as he celebrated Mass at the cathedral on the main plaza, or Zocalo, where police are stationed.

"Each person should be committed to bringing about peace," he said

After federal police backed by water cannons took the city center, demonstrators moved their base to the university, which the under Mexican law the police cannot enter without the permission of the rector. Oaxaca rector Francisco Martinez has said police are not welcome.

Police surrounded the campus on Thursday and battled hundreds of protesters armed with gasoline bombs, stones and fireworks stuffed with glass and nails in a six-hour struggle that left more than 30 people injured.

The Fox administration says the federal troops are neutral in the Oaxaca conflict.

"We do not see them as part of the problem. We see them as part of the solution: to restore a minimal amount of order," Interior Undersecretary Arturo Chavez told foreign reporters Saturday.

On Saturday, masked protesters detained and blindfolded two men near the university, accusing them of being spies for the federal police.

Mexico's Defense Ministry said in a news release Sunday that the men were soldiers who were tied up, beaten and robbed before being released. The Defense Ministry condemned the action but said it maintains its "commitment to the Mexican people" in "staying on the sidelines of the current situation occurring in the capital of the state of Oaxaca."

The protests began in May, when teachers struck for better pay and conditions in one of Mexico's poorest states. When police violently broke up one of their demonstrations in June, protesters expanded their demand to include the ouster of Ruiz and were joined by leftists, Indian groups, students and others.

Among the nine people killed during the Oaxaca conflict was activist-journalist Bradley Roland Will, 36, of New York, who was shot in the stomach while filming a gunbattle on Oct. 27.

Two officials of a municipality on the outskirts of Oaxaca city are in custody in connection with Will's killing, state officials have said.

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