Fergana, Uzbekistan ? Eight Uzbek soldiers and three Islamic militants died in a clash near the Kyrgyz border Sunday and more than 500 Uzbeks fled to safety across the frontier, witnesses said, in spreading violence that further threatened stability in this Central Asia country, a key American ally and host to an important U.S. military outpost.

The explosions of pent-up anger have now hit at least two Uzbek border towns in the volatile Fergana Valley in eastern Uzbekistan. As many as 500 people reportedly were killed Friday in Andijan, Uzbekistan’s fourth-largest city about 30 miles west of the Kyrgyz frontier, when government troops were called in to put down an uprising by alleged Islamic militants and citizens protesting dire economic conditions.

Security was tight Sunday in Andijan as stunned residents cleaned blood off streets guarded by troops and armored vehicles. One man said he saw the bodies of three people apparently killed by a soldier Sunday, two days after government forces put down the uprising.

“The city was burying its victims throughout the entire day, and the people are very angry at the president for his order to open fire at protesters,” said the man, who asked to be identified only by his first name, Ilkhom.

The Uzbek Foreign Ministry on Sunday denied that government forces had opened fire on demonstrators. President Islam Karimov has said 10 government soldiers and “many more” protesters died in the Friday conflict and at least 100 people were wounded.

Since then the government has imposed a near-total news blackout on the region, keeping reporters away from scenes of violence.

Karimov, viewed as one of the most authoritarian leaders still in control of a former Soviet republic, cut his political teeth under the old communist system that brooked no civil disobedience. Before the Soviet Union fell apart in 1991, many regional leaders had ordered military or police attacks against their own people when they massed in protest in places like Georgia, Azerbaijan and Kazakhstan.

But if the estimates of 500 dead hold true and if Uzbek forces were behind the killing — as most reports indicate — Friday’s violence would be one of the worst incidents of state-inspired bloodshed since the massacre of protesters in China’s Tiananmen Square in 1989.

Estimates of the number of civilians killed in Tiananmen Square range from 400 to 800 to several thousand.

Karimov has blamed Islamic extremists for the uprising, in which protesters stormed a prison, freed inmates and then seized local government offices before government troops put the protest down with force.

The violence was Uzbekistan’s worst since gaining independence in 1991.