At least 17 protesters have been killed in renewed clashes with police in central Kiev after a truce agreed on Wednesday broke down, eyewitnesses say.
Witnesses reported live rounds, petrol bombs and water cannon at the main protest site, Independence Square.
A meeting between EU foreign ministers and President Viktor Yanukovych is now under way, officials say, contradicting earlier reports that the ministers had flown out without seeing him.
The EU will discuss sanctions later.
Eyewitnesses quoted by international news agencies say they have counted at least 17, and as many as 21 bodies.
The BBC’s Kevin Bishop, in Kiev, saw five dead bodies in the reception area of the Hotel Ukraine, which all foreign media in the city are using as a base.
Several dozen protesters are using the lobby as a triage centre for wounded, and a priest arrived a short time ago, our correspondent says.
Protesters – some of them armed – have been asking hotel guests for blankets to use as bandages.
Earlier, two armoured vehicles were seen in the street leading towards Independence Square, also known as the Maidan, the centre of the protests in Kiev.
A statement on the presidential website blames the opposition for starting the violence, saying the “calls for a truce and dialogue were nothing but a way for playing for time to mobilise and arm militants from Maidan”.
The foreign ministers of Germany, Poland and France are meeting Mr Yanukovych.
The talks were moved from their original location, for security reasons, officials said, and were at first reported cancelled.
A full meeting of EU foreign ministers and EU foreign police envoy Catherine Ashton will take place later on Thursday.
Sanctions on Ukraine are likely to be discussed, including a possible ban on sales of equipment that can be used for internal repression.
Thursday has been declared a day of mourning for the dead.
Most of the victims died during clashes on Tuesday – the bloodiest day since the unrest erupted in late November.
In other developments:
- Parliament and cabinet buildings have been evacuated because of fears that they could be stormed by protesters.
- As many as half of the 45 Ukrainian athletes at the Olympics in Sochi have left the games to return home, a spokesman for the Ukrainian Olympic committee has said
Russia wants a “strong government” in Ukraine, Prime Minister Dmitry Medvedev said on Thursday, “so that people don’t wipe their feet on the authorities like a doormat”.
- President Yanukovych’s chief of staff has said if sanctions are imposed and the situation escalates, “there is a danger that the country could split into two parts,” the Unian news agency reports.
- Trains between Kiev and the western city of Lviv – one of the protesters’ strongholds – have been suspended, the Interfax-Ukraine news agency reports. A railway spokeswoman said this was because of damage to the lines.
- US President Barack Obama warned there “will be consequences” for anyone who steps over the line in Ukraine – including the military intervening in a situation that civilians should resolve.
The EU has so far refrained from imposing sanctions on Ukraine, preferring to stress dialogue and compromise.
For its part, the US state department announced visa bans on 20 members of the Ukrainian government but did not provide any names.
The media wing of the opposition Udar party, led by former boxer Vitaly Klitschko, said the next round of negotiations with President Yanukovych would resume later on Thursday.
It is not yet clear whether these talks will go ahead.
The far-right Right Sector protest movement said it had not signed up to the truce and there was “nothing to negotiate”.
The protests first erupted in November when President Yanukovych rejected a landmark association and trade deal with the EU in favour of closer ties with Russia.
Since then, the protests spread across Ukraine, with the main demand of snap presidential and parliamentary elections.