The Ukrainian opposition vowed to press on with protests despite an offer of top posts made by President Viktor Yanukovych as protesters took control of another building in the capital Sunday.
Two months after the protests began in November over his decision to back out of an EU pact Yanukovych on Saturday offered to share leadership with Arseniy Yatsenyuk as prime minister and Vitali Klitschko as deputy prime minister in a bid to end the crisis.
Opposition leaders said that they will continue negotiations until other demands are met and aim to take power in snap presidential polls.
Protesters meanwhile scored another victory after taking control of a building in central Kiev by ousting some 200 police forces that used it as base.
In a siege overnight of the Stalin-era exhibition hall called Ukrainian House near the protest zone, protesters threw Molotov cocktails as police responded with stun grenades.
Tensions eased after troops were allowed to exit by a side entrance early Sunday to the cries of "Shame!" from protesters.
The interior ministry later said the minister ordered to "withdraw the reserve unit" and essentially accused protesters of attempting to take the troops hostage.
"The goal of the protesters was taking the policemen captive and exchanging them for arrested or detained activists," the ministry's statement said.
Klitschko, the former boxing star head of UDAR party, said that the protesters did not plan to use the building but would guard its entrances so police did not return.
Officials say three people have been killed in the escalating protests in Kiev over the past week, raising fears of a wider civil conflict as protests have spread to outlying regions of Ukraine in the former Soviet republic's worst crisis since independence in 1991.
The opposition says six people have died.
The Ukrainian presidency said after Saturday's talks with opposition leaders that Yanukovych is willing to shuffle his government and consider constitutional changes that would reduce presidential power and return to a system where the prime minister has more authority.
The president also agreed to initiate a bill to amnesty arrested protesters and to re-consider draconian anti-protest laws passed by parliament this month.
Speaking to tens of thousands packed into Independence Square late Saturday after negotiations, the main opposition leaders were careful to neither accept nor explicitly reject Yanukovych's proposal to share leadership.
"We are not scared of responsibility for the future of Ukraine. We take responsibility and are ready to take the country into the European Union," Yatsenyuk told the cheering crowd.
Yatsenyuk, the 39-year-old leader of Fatherland party, later told reporters the opposition was "not over the moon" about Yanukovych's unprecedented proposals.
"We are not refusing the offer but we are not accepting it either," he said. He later wrote on his Facebook page that the opposition should be the one dictating terms, not the other way around.
Klitschko told protesters that "talks will continue" and the opposition would press for a presidential election due in 2015 to be brought forward to this year.
The protests first erupted in response to Yanukovych's refusal to sign a key deal with the European Union in November and a decision to ally closer with former master Russia.
But they have snowballed into anti-government protests against Yanukovych's four-year rule, which the opposition claims has been riddled with corruption and nepotism.
The authorities have also faced mounting pressure outside Kiev with protesters storming regional administration offices, not just in the anti-Yanukovych west of the country but also north and east of Kiev.
Interior Minister Vitaliy Zakharchenko has bluntly warned that the use of force was a possibility and accused the mainstream opposition of failing to control radicals.
"The events of the last days in the Ukrainian capital have shown that our attempts to solve the conflict peacefully, without recourse to a confrontation of force, remain futile," he said.
In a sign of a possible split within the ruling Regions Party over how to deal with the crisis, however, Ukraine's richest man Rinat Akhmetov said Saturday that dialogue was the only way forward.