At least eight people have died in the clashes since late May.
OAXACA, Mexico (AP) -- Federal police with assault rifles and riot-shields advanced into Oaxaca on Sunday, bypassing or extinguishing barricades of burning tires and tree trunks in this normally picturesque tourist destination wracked by five months of protests and violence.
Officers in bulky black helmets lined a highway just shy of a sign reading "Welcome to Oaxaca" and used fire extinguishers to douse flames at a roadblock abandoned by retreating demonstrators.
Flanked by armored vehicles, water-cannon and bulldozers and with helicopters roaring overhead, they faced a knot of protesters who yelled insults and readied piles of stones to hurl. Some protesters used syringes to pierce their arms and legs, then paint signs decrying the police in blood.
In other parts of the city, columns of police climbed over burned-out cars and moved past hijacked tractor-trailers, buses and other debris used to block streets, marching toward downtown. Instead of offering resistance, many protesters retreated, pledging a massive defensive in the city center.
As police marched by, some residents emerged from their homes cheering and waving white flags.
What began in late May as a teachers strike in this colonial southern Mexican city spiraled into chaos as anarchists, students and Indian groups seized the central plaza and barricaded streets throughout the city to demand the ouster of Oaxaca state Gov. Ulises Ruiz. Police and state forces -- often in plainclothes -- have shot at protesters, setting off clashes in which at least eight people have died.
President Vicente Fox, who leaves office Dec. 1, resisted repeated calls to send federal forces to Oaxaca until Saturday, a day after gunfire killed a U.S. activist-journalist and two residents.
Though some protesters retreated, others fortified their posts at street blockades, pledging a street-by-street defense against the Federal Preventative Police. But Bertha Munoz, one of the movement's leaders, said that many demonstrators were peaceful.
"How can we confront them? We have already seen the R-15 [rifles] and AK-47s they carry," she said. "What do our people have? Most have just come to bring them flowers."
The Interior Department issued an ominous statement demanding that protesters give up their occupation of the city immediately, but officials said Sunday they hoped negotiations could avoid further bloodshed.
Protesters accused Ruiz of rigging his 2004 election and using thugs to kill or intimidate political opponents. They say they will not return home without his resignation.
In Mexico City, several hundred supporters of the Oaxaca protests converged on a hotel where Ruiz was rumored to be staying, damaging the grounds around the entrance and screaming "Murderer! Murderer!"
The government news agency Notimex reported that a vehicle transporting federal police to Oaxaca crashed Sunday, killing one officer and injuring 12. Federal officials could not confirm the report, but protesters cheered wildly as it circulated Oaxaca.
The protesters estimated that around 4,000 federal police had taken up positions around the edges of the city. There were no official reports, however, on how many officers were sent to Oaxaca.
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