Ukraine’s opposition leader Vitaly Klitschko said on Wednesday that he has quit talks with President Viktor Yanukovych without reaching any agreement on how to end the violence in Kiev, local media said.
“Unfortunately, I bring nothing good from the talks,” the Ukrainska Pravda news website quoted Klitschko as saying.
At least 25 people have been killed in fierce clashes between protesters and riot police in clashes that started on Tuesday and continued until early Wednesday – the bloodiest outburst of violence in nearly three months of demonstrations. Many were killed by gunshot, and hundreds more injured, with dozens of them in a serious condition, police and opposition representatives said.
Watch:Clashes, explosions rock Kiev as police storm protest camp
Klitschko said that he left the talks after the president demanded that the central square in Kiev occupied by anti-government protesters be unconditionally cleared.
Yanukovych told opposition leaders that he would not call off a bloody police assault on the opposition’s main protest camp on Kiev’s Independence Square, Klitschko said.
“Yanukovych said that there is only one option … to clear Maidan and that everyone has to go home,” Klitschko told independent Hromadske TV after meeting with the president. Maidan is the name of the main protest camp at the city square, which protesters have fortified with tyres, benches and sand bags.
It was not clear from the report whether talks between the president and the two remaining opposition leaders, including former economy minister Arseny Yatsenyuk, were continuing.
Ukrainian riot police charged protesters  occupying the central Kiev square early on Wednesday. Four protesters were killed during the police assault on the opposition’s main protest encampment on Kiev’s iconic Independence Square where protesters have camped out demanding that Yanukovych leave power.
A police spokeswoman said some of the deaths were caused by a traffic accident, heart attacks and a fire.
Police threw stun grenades and fired water cannons as they battled their way into the square but demonstrators, some armed with clubs and wearing helmets and body armour, tried to stand their ground. Some protesters hurled Molotov cocktails behind the phalanx of anti-riot officers.
The crackdown on Tuesday came after Ukraine’s state security service set a deadline for the demonstrators to end disorder or face “tough measures”. “If by 6pm the disturbances have not ended, we will be obliged to restore order by all means envisaged by law,” the security service and Interior Ministry said.
Smoke billowed from burning tents and piles of tyres and wood as thousands of protesters held on to Maidan, a Reuters cameraman said. Several floors of a trade union building, used as an anti-government headquarters, were on fire.
Prior to the assault on Independence Square, authorities said that five civilians and seven police officers were killed as security forces fought running battles with protesters.
Two other bodies were also found in the area of protests but police said that they did not show any evidence of violence.
Outside the capital, anti-government protesters seized government buildings in a few cities in the western part of the country, local media and the police said on Wednesday.
They seized regional administration headquarters in Ivano-Frankivsk and Lviv, police said. Ukrainska Pravda reported that protesters torched the main police station in Ternopil and were trying to seize the headquarters of regional administration.
Opposition lawmaker Oleksander Aronets said that protesters had also seized the local prosecutor’s office.
The riot police moved in hours after Moscow gave Ukraine US$2 billion  in aid for its crippled economy which it had been holding back to demand decisive action to crush the protests.
Monday’s cash injection, a resumption of a US$15 billion aid package, was seen as a signal that Russia believed Yanukovych had a plan to end the protests and had dropped any idea of bringing opposition leaders into government.
Alarmed Western governments demanded restraint and dialogue. US Vice-President Joe Biden spoke to Yanukovych by phone, urging him to pull back the government forces and exercise maximum restraint, the White House said.
UN secretary general Ban Ki-moon expressed grave concern over the deaths and renewed violence, cautioning the administration to exercise restraint.
Nationwide demonstrations erupted in November after Yanukovych bowed to Russian pressure and pulled out of a planned far-reaching trade agreement with the European Union, deciding instead to accept a Kremlin bailout for the heavily indebted economy.
Western powers warned Yanukovych 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.
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”.
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 raised 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.”
“News of a fresh escalation of violence is alarming. We are shocked to hear of the dead and injured today,” Steinmeier said.
Ukraine has been rocked periodically by political turmoil since gaining independence from the Soviet Union more than 22 years ago, but it had never experienced violence on this scale.