Opposition leader Roza Otunbayeva demanded the resignation of President Kurmanbek Bakiev, whom she helped bring to power five years ago, and told Reuters she would run an interim government for six months.
"We have a caretaker government now in place, and I am the head of it," Otunbayeva said. "It will remain in place for half a year, during which we will draft the constitution and create conditions for free and fair (presidential) elections."
The violent unrest, which spread to Bishkek on Wednesday, was sparked by growing discontent over corruption and rising prices in a nation where a third of the 5.3 million population live below the poverty line.
Bakiyev fled Bishkek to the southern city of Osh, his traditional power base in a nation split by clan rivalries. In the city centre, hundreds of his supporters scuffled with hundreds of opposition demonstrators, a Reuters reporter said.
The government building that Bakiyev left behind in Bishkek was stormed by protesters who smashed trucks through the perimeter fencing.
A Reuters reporter inside the building saw demonstrators walking over broken glass and smashed computers and sending papers cascading from windows. The seventh floor, where the president keeps his office, was badly charred.
"The whole country is on fire," said Nurlan Aslybekov, an unemployed man who travelled to Bishkek from the town of Talas, where the first anti-government protests broke out on Tuesday.
The United States has a military air base supporting troops in Afghanistan in the Kyrgyz city of Manas and is a major donor to Kyrgyzstan, along with China and Russia, which also has military base in the former Soviet state.
State Department spokesman P.J. Crowley said operations at the Manas base - visited by US Central Command chief General David Petraeus last month - appeared unaffected.
"It's an important facility connected to our Afghan operations and it's functioning normally," he said.
Bakiyev came to power in the 2005 'Tulip Revolution' protests, led jointly by Otunbayeva, which ousted Kyrgyzstan's first post-Soviet president, Askar Akayev. She briefly served as acting foreign minister before falling out with Bakiyev.
Spokesmen for the president were not available for comment.
A senior US State Department official said Bakiyev's fate was unclear. "We are in touch with both government officials and the opposition encouraging resolution according to the rule of law," he said, on condition of anonymity.
Gunshot wounds
The opposition said at least 100 people had been killed on Wednesday. A Health Ministry official put the death toll in Bishkek at 65, and said 400 people had been injured.
The violence was the deadliest in former Soviet Central Asia since government forces in Uzbekistan fired on protesters in the city of Andizhan in May 2005. The Uzbek government said 187 people died, including its forces, but rights groups say several hundred mostly unarmed protesters were killed.
Political unrest over poverty, rising prices and corruption has gripped Kyrgyzstan since early March. The average monthly wage is about $130 and remittances from workers in Russia have fallen sharply during the global economic crisis.
"It was a never ending rip-off. Every day they would raise prices for gas, for water, and in the end is it good to shoot at your own people?" said Alioglu Samedov, 62, a retired lawyer.
Analysts said the unrest would also increase uncertainty for foreign investors in Kyrgyzstan's mining sector and raised the possibility of outside military intervention.
"Bakiyev is unlikely to return to power but the prevailing uncertainty poses severe risks to foreign investors, raises the possibility of foreign intervention and will directly affect US interests in Central Asia," Eurasia Group analyst Ana Jelenkovic said.
Shops were still ablaze after a night of looting in central Bishkek. People ran through the streets carrying computers and office equipment, and protesters spat at a portrait of Bakiyev on a large carpet carried out of the government building.
The foreign ministry in China, which shares a border with Kyrgyzstan, said it was "deeply concerned" about the unrest.
"Kyrgyzstan's situation returning to normal as soon as possible is in the interest of the Kyrgyz people, as well as in the interest of regional peace and stability," spokeswoman Jiang Yu said in a statement on the ministry website www.fmprc.gov.cn.
Russian Prime Minister Vladimr Putin earlier called for calm and denied Moscow had played a hand in the clashes.
"Neither Russia, nor your humble servant, nor Russian officials have any links whatsoever to these events," Putin was quoted as saying by RIA news agency.
(EurActiv with Reuters.)
