Kyrgyzstan's president, Askar Akayev, has ordered a review of some parliamentary poll results amid growing protests over alleged irregularities.
Security forces flee one building in Osh as protests mounted
His office said a review would be held in districts of the Central Asian state where the poll results had sparked "a strong public reaction".
The announcement came as opposition protesters seized two towns, including the country's second city Osh.
Russia's Foreign Ministry condemned the protests, blaming "extremists".
"Extremist forces must not be allowed to use political instability to create a threat to the democratic foundations of the Kyrgyz statehood," it said in a statement.
Russia also rebuked the Organization for Security and Cooperation (OSCE) for declaring that the elections had fallen short of democratic standards.
It urged the body to be "more responsible" in its election monitoring conclusions "to prevent destructive elements from using these assessments to justify their lawless actions".
Kyrgyzstan hosts a US and a Russian military base on its soil - the former set up after the collapse of the Soviet Union.
Protests in the south of the country started after run-off elections on 13 March.
The opposition had only won a handful of seats in the nation's 75-seat parliament.
Demonstrators are now trying to force the Soviet-era president, who was first elected in 1990, to step down.
A spokesman for Mr Akayev on Monday said he was ready to hold talks with the opposition.
"The most important thing right now is to let people calm down, assess what has happened and then start negotiations with them about their demands," Reuters news agency reported the spokesman as telling Kyrgyz television.
The protests have drawn comparisons with other popular upheavals in the former Soviet states of Georgia and Ukraine, although Mr Akayev has warned that such an development would risk civil war in Kyrgyzstan.
On Monday, some 1,000 protesters stormed the regional government building and police headquarters in Osh and forced police to flee.
The BBC's Central Asia correspondent, Monica Whitlock, says most security forces seem to have escaped unhurt, but rioters caught two, beat them up, and paraded them on horseback around the square.
The demonstrations came after about 10,000 people besieged and then burnt down the police station in Jalal-Abad on Sunday and blocked the airport's runway to prevent the government flying in re-enforcements.
Call for talks
Four officers were beaten to death, police sources told Reuters news agency.
"The people are gathering their strength," Kubanishbek, a 47-year-old farmer told AFP news agency at a rally in Jalal Abad's main square attended by some 3,000 people.
"The aim is to kick out Akayev. The power should be in the hands of the people."
Kyrgyzstan's Prime Minister Nikolai Tanayev said the government was ready to talk to the protesters, and promised that force would not be used.
"Not the president, not me, and not the interior minister will allow weapons to be used against our own people," he said.
But an opposition leader said talks would only be worthwhile if President Akayev himself took part.
Police have been holding back protesters for several days
"All other lower level negotiations will be just a waste of time," Kurmanbek Bakiyev of the People's Movement of Kyrgyzstan told the Associated Press news agency.
The latest protests are also taking place in a highly sensitive region, close to the border with Uzbekistan.
A sizeable proportion of the region's population is ethnically Uzbek. They, along with some ethnic Kyrgyz in the south, are unhappy with the government's handling of the economy, and perceived corruption.