Twelve people were killed when violence erupted in Kyrgyzstan's second-largest city Osh on Friday, prompting the interim government to declare a state of emergency and send in armored vehicles.
Hundreds of youths fought with steel bars and set shops and cars ablaze.
The government, led by Roza Otunbayeva, described it as a "local conflict" possibly sparked by an argument in a casino, but the violence in the southern power base of former President Kurmanbek Bakiyev was likely to stoke fears of ethnic clashes.
Bakiyev was deposed in April as leader of the impoverished Central Asian country in a popular revolt that raised concern among regional players Russia, China and the United States. The country hosts both a Russian and a U.S. military base.
His supporters briefly seized government buildings in the south on May 13, defying central authorities in Bishkek.
Twelve people were killed and scores were injured in Friday's violence, some with gunshot wounds, a Health Ministry spokeswoman said.
The Interior Ministry said five people had been detained and that the situation in Osh was "strained." A ministry spokesman said preliminary information suggested the violence could have started in a casino.
Several shops were still on fire near the mayor's office in central Osh, a Reuters witness said. A crowd had gathered and gunfire could be heard.
The interim government declared the state of emergency in Osh and three surrounding regions after holding an emergency meeting in the early hours of Friday, a spokesman for the government said.
"Roza Otunbayeva announced that the interim government will deploy all of its available resources and is sure that security will be provided for its citizens," the spokesman, Farid Niyazov, said by telephone.
Ismail Isakov, defense minister in the interim government, flew to Osh immediately after the emergency meeting. Isakov was recently appointed by the interim government as its special representative for southern Kyrgyzstan.
Interior Minister Bolot Sherniyazov has also flown to Osh, a city of more than 200,000 people in the volatile Fergana valley.
Niyazov said between 1,000 and 3,000 people had been involved in the overnight violence, fighting with steel bars and their bare hands in the streets.
"More than 500 people have arrived in hospital overnight with knife wounds," a doctor at a hospital in Osh told Reuters on condition of anonymity.
The crowds dispersed after troops and armored vehicles were sent into the city, Niyazov said. He said the state of emergency would remain in force until June 20.
Kyrgyzstan, which won independence with the collapse of the Soviet Union in 1991, has been in turmoil since the revolt that toppled Bakiyev on April 7, kindling fears of civil war.
Political tensions between the agricultural south and the north of Kyrgyzstan exist alongside ethnic and clan rivalries.
Behind the turmoil
Ethnic unrest between Kyrgyz and Uzbeks is a concern in the Fergana valley where Kyrgyzstan and Uzbekistan intertwine.
Two people were killed and 74 were wounded on May 19 in clashes between Kyrgyz and Uzbeks in the city of Jalalabad. On the same day, Otunbayeva said she would rule the country until 2011, scrapping earlier plans for presidential polls in October.
Jalalabad has also been the scene of fierce clashes between supporters of the interim government and those of Bakiyev, who is in exile in Belarus.
The Fergana valley, which also includes parts of Tajikistan, is a particularly volatile part of Central Asia. In 1990, shortly before the collapse of the Soviet Union, hundreds of people were killed in ethnic clashes near Osh.
Of Kyrgyzstan's 5.3 million population, ethnic Kyrgyz make up 69.6 percent, Uzbeks 14.5 percent and Russians 8.4 percent.
The mix is more even in the south. Uzbeks comprise about 40 percent of the 1 million population in the Jalalabad region and about 50 percent in the neighboring region of Osh.