The official death toll rose to more than 100, and thousands of refugees poured across the border into Uzbekistan as the authorities were unable to contain the murderous mobs.
Whole sections of Osh, where longstanding tensions between the Kyrgyz majority and the Uzbek minority exploded into violence Thursday night, were all but deserted on Sunday, and heavy black smoke still billowed from Uzbek enclaves set afire by Kyrgyz gangs.
Heavily armed police officers guarded intersections, and troops patrolled in tracked artillery vehicles, but few pedestrians or motorists were visible.
On a block once shaded with trees, the roofs were caved in and windowsills were seared with black smoke, testament to a campaign of rage that moved from house to house through an Uzbek neighborhood. Only one building was left untouched: a squat convenience store that had been spray-painted with the word “Kyrgyz” in red.
By Sunday night, Osh was tense but quiet as the authorities appeared to have had some success in restoring order. But the situation remained volatile, and the unrest still threatened the fragile provisional government in this country, which hosts a critical American military base.
“There is sorrow, so much sorrow here,” the Osh regional governor, Sooronbai Jeenbekov, said in an interview. “I don’t have the words.”
According to reports from villages and towns across the region, bands of Kyrgyz had sought out Uzbeks, setting fire to their homes and killing them. Tensions between Kyrgyz and Uzbeks have erupted before, and appear to have been reignited by the ouster of the president in April. Local Uzbeks largely support the country’s new leadership in a predominantly Kyrgyz stronghold of the former president, Kurmanbek Bakiyev.
The provisional government has accused Mr. Bakiyev of provoking the violence in order to destabilize the country. On Sunday, Mr. Bakiyev, who is in exile in Belarus, issued a statement saying that he had played no role in the violence.
A Kyrgyz official estimated that more than 10,000 Uzbeks had fled across the border to Uzbekistan. The government of Uzbekistan estimated the figure at 75,000, saying that it had set up refugee camps on its side of the border.
Uzbeks make up about 15 percent of the overall population of Kyrgyzstan, but they are represented in much higher numbers in Osh, which has roughly 225,000 people and is on the Uzbek border.
Uzbekistan and Kyrgyzstan have repeatedly clashed over land and water in the fertile Fergana Valley, which Stalin divided among Uzbekistan, Kyrgyzstan and Tajikistan. The valley remains an ethnic patchwork, and minority enclaves, like that of the Uzbeks in Osh, have been scenes for violence.
While the violence had ebbed in Osh on Sunday, the military and the police had not completely regained control. Some roadways leading to the city were patrolled by crowds of young men armed with Kalashnikov rifles and bats topped with knives.
Otherwise, there was little sign of life apart from stray dogs that trotted through the streets, though hundreds or possibly thousands of Uzbeks were barricaded in their ravaged neighborhoods, communicating with the outside world via phone calls and text messages.
One resident of an Uzbek neighborhood said all food had been stripped or stolen from the stores, and there were rumors that poison had been added to the water supply. But he said violence had subsided significantly since Saturday, when two people were killed by snipers.
While small and impoverished, Kyrgyzstan is strategically important because it is host to an American military base, Manas, that supports the NATO mission in Afghanistan. Russia also has military facilities in the country. Both countries have been concerned about the interim government’s stability, and its failure to maintain control over the south in recent days has thrown its fate into doubt.
On Saturday the government asked Russia to send peacekeeping troops, but Russia, which has been a political patron of this former Soviet republic, said only that it would consider the request. On Sunday, Russia did send paratroopers to protect its military facilities in Kyrgyzstan.
The interim government, led by Roza Otunbayeva, has sent volunteers to the south and authorized security officers to use deadly force to quell the riots.
The mobs that rampaged through Osh seemed to be meticulous in singling out Uzbek property, judging from the smattering of intact buildings marked “Kyrgyz” or “KG,” some with curtains still hanging in the windows. Those cars that remained were burned out and flipped over, and columns of trucks were seen Sunday hauling loads of them out of the city.
The streets were still scattered with burnt tires and trees that had been cut down to form makeshift roadblocks. It was unclear how many residents remained.
Homemade video shot on Saturday in Osh showed scorched bodies lying side by side along the street, some bound with makeshift bandages, and the burnt, overturned shells of passenger cars.
Residents were shown using small plastic buckets to throw water into the smoking wreckage of razed buildings in a hopeless attempt to save some of the interiors. Women made their way by foot out of the city, carrying practically nothing and leading children by the hand.
The rioting could pose a challenge to the legitimacy of the unelected provisional government, formed by several opposition figures in April. Political analysts said a hard-line politician could try to seize power, arguing that the current leaders had been ineffectual in ending the unrest.
A Russian-backed news Web site in Kyrgyzstan, Bely Parus, appeared to withdraw support for the interim leader, Ms. Otunbayeva, over the weekend. Russia still has considerable influence in the country’s internal politics, and has been an enthusiastic supporter of the new government.
The Web site published an editorial saying that politicians not in power should make sure that peacekeepers are brought into Kyrgyzstan, if Ms. Otunbayeva is not successful in doing so.
Bely Parus reported that a former prime minister, Felix Kulov, who is not in the interim government, had formed a group under the slogan “Whoever Values Peace — Unite!” that was gaining traction.