The Ukrainian president has blamed the country's opposition for the bloodshed in Kiev's Independence Square after 25 people were reportedly killed in the city's most violent clashes since the former Soviet republic won its independence.
Anti-government protesters, many of them masked, have poured back onto the streets this morning, preparing to confront police for a second day.
Viktor Yanukovich released a statement on Wednesday, saying opposition leaders "crossed a line when they called people to arms" as riot police battled with protesters occupying the square.
Mr Yanukovych said opposition leaders had to "draw a boundary between themselves and radical forces," or else "acknowledge that they are supporting radicals". He warned: "then the conversation ... will already be of a different kind."
The defiant tone of the statement quashed hopes of a compromise to resolve the crisis, which erupted three months ago when Yanukovich decided against signing a free trade and association agreement with the European Union, choosing instead to increase ties with Russia.
Police were gaining ground after hours of clashes in the square but demonstrators managed to hold their defence lines behind a burning barricade of tires and wood.
Shrouded in plumes of black smoke, police attempted to extinguish the fire with two water cannons but protesters responded by hurling petrol bombs at the police vehicles, a Reuters cameraman said.
Police have gained control of almost half the square and several floors of a trade union building, used as an anti-government headquarters, were engulfed in flames as dawn was breaking.
At least 14 protesters and seven policemen died in violence that erupted yesterday and continued into the early hours of today. The Ukrainian health ministry put the number dead at 25 this morning.
Many were killed by gunshot and hundreds of people were injured, with dozens in serious condition, police and opposition representatives said.
Alarmed Western governments demanded restraint and dialogue. US Vice President Joe Biden called Yanukovich, urging him to pull back government forces and exercise maximum restraint, the White House said.
Opposition leaders Vitali Klitschko and Arseny Yatsenyuk said that they had ended talks with President Viktor Yanukovich without coming to a joint agreement on how to resolve the crisis.
“The government must immediately withdraw troops and put an end to the bloody conflict, because people are dying. I told Yanukovich this,” Klitschko said after the late night talks. “How can we hold talks while blood is being shed?”
The unrest has spread to at least three cities in the western part of the country. Police said protesters had seized regional administration headquarters in the cities of Ivano-Frankivsk and Lviv. Media said protesters torched the main police station in the city of Ternopil.
The authorities have restricted traffic coming into the capital to prevent reinforcements from reaching protesters and shut down the underground.
Earlier, the state security service set a deadline for the demonstrators to end disorder or face “tough measures”. Then the police advanced to the square before launching a full assault in the early hours, throwing stun grenades and using water cannons.
Western powers warned Yanukovich against trying to smash the pro-European demonstrations, urging him to turn back to the EU and the prospect of an IMF-supported economic recovery, while Russia accused them of meddling.
“We are now facing of one of the most dramatic episodes in Ukrainian history,” opposition leader Yatsenyuk said in a video message after emergency talks with the president failed.
As the security forces moved forward, Klitschko, a former world champion boxer, reacted defiantly, telling supporters on the square: “We will not leave here. This is an island of freedom. We will defend it.”
Earlier yesterday, the State Security Service (SBU), in a joint statement with the Interior Ministry, signalled the government's intentions. “If by 6 pm the disturbances have not ended, we will be obliged to restore order by all means envisaged by law,” they said.
The riot police moved in hours after Moscow gave Ukraine $2 billion in aid for its crippled economy that it had been holding back to demand decisive action to crush the protests.
EU Enlargement Commissioner Stefan Fuele said he had spoken to Ukraine's acting prime minister, who had given assurances that the authorities would try to avoid using live firearms.
“For the sake of the Ukrainians and for the sake of the future of that country, I will pray that he is right,” Fuele told a public event in Brussels.
Right Sector, a militant far-right group, added to tension by urging people holding weapons to go to Independence Square, also known as Maidan, to protect it from the security forces.
As protesters and police battled, Russia called the escalation a “direct result of connivance by Western politicians and European structures that have shut their eyes ... to the aggressive actions of radical forces”.
UN Secretary-General Ban Ki-moon called for restraint, said his spokesman, Martin Nesirky, adding: “He is extremely concerned over today's reports of renewed violence and fatalities.”
EU foreign policy chief Catherine Ashton, who has tried to broker a power-sharing transition, urged Ukraine's leadership “to address the root causes of the crisis”.
Germany's foreign minister, Frank-Walter Steinmeier, telephoned his Ukrainian counterpart to warn against sliding back into violence and to urge the government to keep working for a political solution.
“News of a fresh escalation of violence is alarming. We are shocked to hear of the dead and injured today,” Steinmeier said in a statement, raising the possibility of EU sanctions against Ukrainian leaders.
“Those responsible for taking any decisions that lead to the further spilling of blood must know that the reserve Europe has shown in terms of personal sanctions will be reconsidered.”
Monday's $2 billion cash injection, a resumption of a $15 billion aid package, was seen as a signal that Russia believed Yanukovich had a plan to end the protests and had dropped any idea of bringing opposition leaders into government.