The protesters said the demonstrator had died of gunshot wounds during the clashes.
This was not immediately confirmed by the Ukrainian authorities, but a Reuters cameraman was shown the body of a man identified as a protester who had gunshot wounds, Reuters reported.
The witnesses said police had tried to dismantle a protest camp set up by demonstrators angered by Yanukovich's decision to shun a trade pact with the European Union. Police fired teargas and the protesters threw petrol bombs.