Witnesses said fighting broke out on Thursday night between ethnic Kyrgyz and Uzbek groups in Osh, a stronghold of Kurmanbek Bakiyev, the president who was overthrown by a popular revolt in April.
'Difficult to decline'
Al Jazeera's Laurence Lee, reporting from Moscow, said Kyrgyzstan's public appeal for help could make it difficult for Russia to decline.
"Medvedev had said on Friday that he thought the Kyrgyz could try to sort this out by themselves. Clearly, [the Kyrgyz] are saying they can't do that," he said.
"If they did refuse given the violence, it would make them look quite hard-heartened, not the least to the domestic population in Russia who would be very supportive of Russian peacekeepers going in.
"It would demonstrate that Russia is still a player and it still has sway over its former territories."
Meanwhile, Al Jazeera's Robin Forestier-Walker, speaking from outside the city of Osh, said thousands of ethnic Uzbeks, mostly women and children, were fleeing their homes on Saturday, in an attempt to cross the border into Uzbekistan.
"Behind them, I can see the city of Osh with a huge [plume] of smoke above it. In front of us, we have the border and guards... [and] the people are absolutely desperate.
"I have to say it is a one-sided story that I'm able to provide at this stage, because we are also trapped here - it's too dangerous to get elsewhere in the city at the moment.
"But what's clear is that thousands of people have been massing on the Kyrgyz-Uzbek border and the Uzbek security guards have started letting people through."
Our correspondent in Kyrgyzstan said the situation in Osh was still precarious on Saturday.
"From speaking to eyewitnesses on the phone, people are still having their homes torched and many residents are trapped in their neighbourhoods because of makeshift barriers and barricades," he said.
"I cannot confirm who is doing the killing. We haven't been able to get the version of events from the interim government."
Otunbayeva's government imposed a state of emergency in the region on Friday, after several buildings across Osh were set ablaze after overnight fighting.
"A state of emergency has been declared in Osh and these districts from June 11 until June 20," Farid Niyazov, a government spokesman, said, referring to the neighbouring districts of Karassu, Arava and Uzgen.
Kyrgyzstan, which won independence with the collapse of the Soviet Union in 1991, has been in turmoil since the revolt that toppled Bakiyev, who is in exile in Belarus.
Political tensions between the agricultural south and the north of Kyrgyzstan exist alongside ethnic and clan rivalries.
Bakiyev's supporters briefly seized government buildings in the south on May 13, defying central authorities in the capital, Bishkek.
Two people were killed and 74 were wounded on May 19 in clashes between Kyrgyz and Uzbeks in the city of Jalal'abad. On the same day, Otunbayeva said she would rule the country until 2011, scrapping earlier plans for presidential polls in October.
Of Kyrgyzstan's 5.3 million population, ethnic Kyrgyz make up 70 per cent, Uzbeks 15 per cent and Russians 8 per cent.