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.
Earlier, two armoured vehicles were seen in the street leading towards the Maidan, the centre of the protests in Kiev.
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.
Sanctions on Ukraine are likely to be discussed, including a possible ban on sales of equipment that can be used for internal repression.