The government in Kyrgyzstan is struggling to retain power as deadly clashes escalate between police and thousands of protesters.
Officials say at least 40 people died in the capital, Bishkek, as protesters stormed government and TV offices.
The protesters are angry at rising prices and accuse President Kurmanbek Bakiyev of failing to curb corruption.
A key opposition leader has said the government has now resigned but there is no official confirmation.
The leader, Temir Sariyev, said Prime Minister Daniyar Usenov had agreed to tender the government's resignation and that Mr Bakiyev had left Bishkek.
Mr Sariyev said a new "people's government" had been formed, headed by a former foreign minister, Roza Otunbayeva.
The Agence France-Presse news agency quoted an airport employee as saying that Mr Bakiyev had flown out of Bishkek aboard a small plane.
A senior opposition figure, Galina Skripkina, told Reuters news agency the president had flown to the southern city of Osh.
However, the Russian RIA news agency quoted a government source as saying the president was still in the city.
The US state department, meanwhile, said it believed the Kyrgyz government "remains in power".
The opposition has taken control of at least one television channel.
Another opposition leader, Omurbek Tekebayev, said in a broadcast that at least 100 demonstrators had been killed in the clashes.
A Kyrgyz human rights activist, Asel Kuttubayeva, said on the channel that several regional administrations had been seized and their governors had resigned.
None of the claims on the broadcasts can be independently confirmed.
The health ministry said 40 people had died and more than 400 were injured in the clashes.
One doctor in Bishkek, Akylbek Yeukebayev, told Reuters there were "dozens of dead bodies, all with gunshot wounds".
Kyrgyzstan, a strategically important Central Asian state, houses a key US military base that supplies forces in Afghanistan. Russia also has a base there.
The US embassy in Bishkek and Russia have both expressed concern and called for restraint.
Mr Putin denied Moscow had played any role in the clashes.
"Neither Russia, nor your humble servant, nor Russian officials have any links whatsoever to these events," the RIA news agency quoted him as saying.
A spokesman for Ban Ki-moon said the UN secretary general was "shocked by the reported deaths and injuries that have occurred today in Kyrgyzstan. He urgently appeals for dialogue and calm to avoid further bloodshed".
Bloodstains
The unrest broke out in the provincial town of Talas on Tuesday and spread to Bishkek and another town, Naryn, on Wednesday. All three were put under curfew.
Interior Minister Moldomusa Kongatiyev, who was believed to have gone to Talas to calm the situation, was reportedly severely beaten.
Some reports said he had been killed by the mob, others that he was taken hostage, but there is no confirmation of his fate.
In Bishkek, protesters attempted to storm the president's office but were held back by security forces, who reportedly fired live rounds into the crowd.
Earlier, police had used tear gas and stun grenades to try to break up crowds outside an opposition headquarters but the protesters overcame the police and marched to the presidential offices in the city centre.
Police cars were overturned and set alight and officers attacked by the crowd, some of whom were armed.
Gunfire could be heard crackling through the centre of Bishkek and photographs from the city showed bloodstains on the pavement. The prosecutor's office was also set alight.
Mr Sariyev had been arrested after arriving on a flight from Moscow on Wednesday and a number of other opposition leaders were also detained.
Protesters freed Mr Sariyev on Wednesday and there are unconfirmed reports that up to 10 leaders have now been released.
Mr Bakiyev came to power amid a wave of street protests in 2005 known as the Tulip Revolution, but many of his allies have deserted him claiming intimidation and corruption.
AT THE SCENE
Rayhan Demytrie, BBC News, Bishkek
We've been to the square where the demonstrations were taking place - the situation is very chaotic.
There are thousands of people there, mainly young men, and lots of them have arrived from different parts of Kyrgyzstan.
They are very angry and it was very noisy, the police were firing stun grenades and also live rounds. We saw people who had been shot - one man walked past me, he had been shot in the hand.
We seemed to be the only camera there - and the protesters wanted us to see the people who had been killed. We saw at least one dead man.
All this has angered the protesters even further - they say they won't go anywhere and were shouting "the president must go".
KYRGYZSTAN FACTS
One of the poorest of the former Soviet states
Hosts both US and Russian military air bases
Population mostly Kyrgyz but 15% are Uzbek and a significant number of Russians live in the north and around the capital
Kurmanbek Bakiyev has been president since the Tulip Revolution of 2005, which overthrew the government of Askar Akayev
Mr Bakiyev vowed to restore stability but has been accused of failing to tackle corruption
Opponents also complain he has installed relatives in key government posts
Domestic media have come under increasing pressure from the government in recent months
BBC News
