Flowers dotted the streets and freshly dug graves scarred the earth across this eastern Uzbek city Monday as residents mourned what witnesses said were hundreds killed by security forces last week — the worst unrest since the former Soviet republic won independence in 1991.

New reports emerged that violence in nearby towns killed hundreds more, further threatening the stability of the government of President Islam Karimov (search), a key U.S. ally in the war against terrorism.

The violence puts the United States in a difficult position because it relies on Karimov's authoritarian government for an air base in the country and anti-terrorism support.

Secretary of State Condoleezza Rice (search) said Monday the United States was "still trying to understand" what happened in Andijan (search), Uzbekistan's fourth-largest city, where government troops put down a prison uprising by alleged Islamic militants and a demonstration by citizens about dire economic conditions.

"This kind of problem is also going to be helped if you can get a more open political system in Uzbekistan. They really need more political reform and we've been saying that to the Uzbeks for some time," Rice said. "I don't mean that they should tolerate terrorists or terrorist groups. ... But it is a system that is politically too closed."

"The main preoccupations are now to encourage everybody to forgo any further violence, to help with the refugees that went into Kyrgystan out of Uzbekistan, and to try to deal with the consequences right now of this set of issues," she said.

The government has blamed Islamic extremists for the violence. The crackdown came after protesters stormed a prison, freed inmates and then seized local government offices. But many of the demonstrators were citizens complaining about poverty and unemployment.

Karimov's government has denied firing on demonstrators. However, an Associated Press reporter and other journalists witnessed troops opening fire on the crowd at Andijan's central square.

Channel One state television aired a report alleging militants in Andijan had fired at civilians. Khushnudbek Matmusayev, a medical doctor, told Channel One that the militants had fired at an ambulance, killing two medics and a driver.

It is unknown how many died in Friday's violence.

A respected local doctor in Andijan told the AP that about 500 bodies were laid out at a school for collection by relatives. There was no independent confirmation of the claim by the doctor, who spoke on condition of anonymity out of fear for her safety; other witnesses have said 200 to 300 were killed when troops put down the uprising Friday.

Saidjahon Zaynabitdinov, head of the local Appeal human rights advocacy group, said Monday that government troops killed about 200 demonstrators on Saturday in Pakhtabad, about 20 miles northeast of Andijan. There was no independent confirmation of his claim.

In Andijan, several bouquets of flowers dotted the middle of one of the city's main streets. Buildings along the road were pockmarked by scattered bullet holes.

On a side street, a dozen Uzbek men wearing black-and-white embroidered skullcaps sat on benches in front of their homes, holding a mourning vigil in line with local tradition.

According to the men, Said Shakirov, a furniture-maker, had heard the commotion late Friday and went to see what was happening. Shakirov, 33, was shot on a main street and tried to make it back to his home but was stopped again by soldiers just 75 feet from his house.

Troops fired on Shakirov again when he refused to stop moving after he pleaded to go home to tend to his wounds, they said.

One resident, Ilkhom, who gave only his first name out of fear for his safety, said Shakirov bled to death while begging for help for hours. The soldiers refused to let anyone leave their homes to assist him.

"No one could help him," Ilkhom said, pointing at several bullet holes in windows, a fence and on a gate on the street next to a patch of gravel where Shakirov died.

Andijan was quiet Monday after a night of gunfire. Residents said government troops were fighting militants in Bogishonol, an outlying district of the city, but the claim could not be confirmed.

A U.N. official, speaking on condition of anonymity for fear of compromising his position, said government troops were concentrating Monday near the city of Namangan, site of the regional airport and a major transport hub in the Fergana Valley.

Troops and armored personnel carriers formed a tight circle around the city center in Andijan. Men were digging graves, including one that appeared to be a large common grave, at neighborhood cemeteries under the watch of Uzbek security service agents.

Zaynabitdinov, the rights advocate, displayed a bag with about a dozen dirty sandals he collected at the center of Friday's violence, some stained with blood, and said the street had been filled with shoes and clothes from those gunned down.

"These were poor people. They weren't terrorists," he told the AP.

He also had a bag full of spent Kalashnikov cartridges and much larger-caliber shells fired from armored personnel carriers, which were used by government forces to quell the protests.

In the capital, Tashkent, several rights activists and opposition politicians, surrounded by scores of uniformed police and plainclothes security agents, laid flowers at a monument to commemorate the victims of violence in Andijan.

Participants accused Karimov of giving orders to shoot at the crowd in Andijan.

"It's clear that they wouldn't have opened fire without an order from the top," said Inera Safargaliyeva, the head of the Committee for Freedom of Speech and Expression.