Ukrainian opposition leaders have vowed to continue their struggle hours after President Viktor Yanukovych offered them two senior posts to defuse a widening crisis.
Addressing supporters on January 25 in Kyiv, Vitali Klitschko repeated opposition calls for snap presidential elections and changes to the constitution.
Arseniy Yatsenyuk said the opposition was ready to take on responsibility but added the "people will determine the power in Ukraine."
Earlier, Yanukovych offered Yatsenyuk the post of prime minister and Klitschko the post of deputy prime minister for humanitarian affairs to defuse protests that are now spreading from Kyiv to other parts of the country.
Yanukovych also agreed to consider changes to the constitution, which currently gives most powers to the president.
"We are not throwing out the proposal, but we are not accepting it, either. We are conducting serious consultations among three opposition forces," Yatsenyuk said later at a news conference in Kyiv.
"To be honest we were not happy about the proposal. I am perfectly aware about what is going on in the country now. The country is on the verge of bankruptcy. They've robbed the country in the past three and a half years to the extent that the treasury is empty. The country has been driven by them into total chaos. And that's why they want to escape responsibility and are waiting to hear from us," Yatsenyuk explained.
He also said the opposition would demand the government sign a free trade agreement with the European Union and free political prisoners, including former Prime Minister Yulia Tymoshenko.
WATCH: Arseniy Yatsenyuk Rejects Yanukovych's Offer
About an hour after the opposition leaders addressed supporters, some demonstrators began attacking a building about 100 meters from Independence Square -- center of the protests -- where police were stationed, smashing windows, breaking doors and hurling firebombs.
According to the AP news agency, the assault on Ukrainian House started after an estimated 200 police were seen entering the building and speculation spread that they were preparing to disperse demonstrators.
The protesters later in the night formed a corridor on the steps of the building to allow security forces inside to leave. According to the AFP news agency, all had left over a few hours.
During a visit to Warsaw on January 25, European Union President Herman Van Rompuy condemned the "use of force and brutality by the Ukrainian authorities against demonstrators."
Earlier, Ukrainian authorities confirmed one more antigovernment protester has died as a tense standoff between protesters and riot police continues in Kyiv and unrest spreads throughout the country.
Kyiv's city health department said the man died on January 25 of injuries sustained in violent clashes earlier this week. His death brings to four the number of confirmed fatalities since violent clashes began in the capital six days ago.
Also on January 25, Human Rights Watch (HRW) released a statement saying it was "gravely concerned" about the life and safety of missing activist Dmytro Bulatov, who has been a prominent figure in antigovernment protests.
The rights organization said Bulatov told his wife he was going to a meeting at 7 p.m. local time on January 23. That was the last contact anyone had with him.
Friends and relatives said his cell phone ceased working the next morning and his car is missing.
HRW cites another opposition activist as saying Bulatov had been receiving threatening text messages for weeks.
Meanwhile, the situation was mostly calm in Kyiv early on January 25 after sporadic clashes overnight. Protesters occupied the Energy Ministry building, but left after several hours.
Police accused protesters of holding two police officers captive in Kyiv's city hall which protesters have occupied, and demanded their immediate release.
Protesters deny they are holding the officers.
A protester shouts to riot police in front of a barricade during an antigovernment protest in downtown Kyiv.
Interior Minister Vitaliy Zakharchenko said efforts to end the crisis peacefully without the use of force remain "futile."
Zakharchenko accused the mainstream opposition of failing to control radicals and claimed protesters were "hoarding firearms" at the Kyiv city hall.
However, in an exclusive interview with the Russian news agency ITAR-TASS, Ukraine's Defense Minister Pavel Lebedev ruled out using the country's military to resolve the protests.
"The army will strictly follow the constitution and laws of Ukraine that clearly lay out its role, functions and tasks," Lebedev said on January 26.
He also rejected claims that the military would intervene in the current conflict, calling such comments "provocations."
Meanwhile, Ukraine's richest man, Rinat Akhmetov -- a key backer of President Viktor Yanukovych -- has said the use of force was "unacceptable."
On January 25, protesters stormed the regional administration offices in the town of Vinnytsia, southwest of Kyiv. Protesters are already occupying government offices in several cities in western Ukraine.
WATCH: Protesters Storm An Administration Building In Vinnytsia
Outside the country, Pope Francis has called for an end to violence in Ukraine and urged "constructive dialogue" between Ukraine's authorities and the people.
"I am close to Ukraine in prayer, in particular to those who have lost their lives in recent days and to their families," he said on January 26.
The pontiff appealed for the "spirit of peace and search for the common good" to prevail in Ukraine.
EU Enlargement Commissioner Stefan Fuele, in Kyiv to try to mediate a solution, urged the government to take concrete steps to halt the violence.
Fuele met on January 24 with both Yanukovych and the three main opposition leaders.
Yanukovych has promised to reshuffle his government, an amnesty for detained protesters, and amendments to laws restricting protests whose passing last week triggered the recent clashes.
But he also said on January 24 he would use all legal measures to end protests.
"First of all, I don't want people to be frozen in the streets. They suffer and they don't know how to get out of this situation. And I will repeat myself -- if we can do it in a good way to stop the radicals we will, if not, we will use all measures under the law. But it's all for the people. There is no other way," Yanukovych said.
PHOTO GALLERY: Protests Spread Beyond The Capital
Burning tires are piled up on the motorway to block the international E40 highway in Novoyavorivsk.
Antigovernment protesters clash with riot police at the regional administration headquarters in the town of Vinnytsia, some 200 kilometers southwest of Kyiv.
Antigovernment protesters at the regional administration headquarters in the town of Vinnytsia
Antigovernment protesters hold a rally near the regional administration headquarters in Vinnytsia.
A protester warms himself near a fire at a barricade close to the regional administration building in Lviv.
A protester stands on a barricade in downtown Kyiv.
A protester protects himself from a fire as he sits on the roof of a burned-out bus in downtown Kyiv.
Antigovernment protesters gather at a barricade at the site of earlier clashes with riot police in Kyiv.
In the town of Chernivtsi in southwestern Ukraine, antigovernment protesters gather outside the regional administration headquarters, with police standing guard.
Protesters enter Chernivtsi's regional administration headquarters.
In the town of Ivano-Frankivsk, a police officer bows his head as he leaves the regional administration headquarters, which protesters attempted to take over.
The opposition had dismissed Yanukovych's promises and wants him to resign. Opposition leader Vitali Klitschko said "to change just the ministers in not enough."
"People want to change the rules because they are already tired of living without rules. Everybody is saying 'no.' You can buy any court, you can't find justice in our country. The system is totally corrupt. And that is why people right now are not happy," Klitschko said.
The antigovernment protests began after Yanukovych unexpectedly pulled back from a long-negotiated agreement on closer ties with the European Union in late November.
They have been fueled by what activists say is widespread government corruption, abuse of power, and the violation of human rights.
With reporting by AFP