KIEV, Ukraine — A deepening civil uprising in Ukraine turned deadly on Wednesday, and this embattled capital veered toward chaos, after at least three demonstrators died during clashes with the police and the first direct negotiations between President Viktor F. Yanukovich and opposition leaders yielded only threats and ultimatums.

As Mr. Yanukovich met the three principal opposition leaders at the presidential headquarters on Wednesday afternoon, protesters and the police battled on a main street near the Dynamo soccer stadium. Flames from burning tires leapt into the air, beneath billows of black smoke, and there were sporadic explosions and gunfire, as the standoff entered its third day.

Two protesters were shot and killed early Wednesday during the violence, the general prosecutor’s office said in a statement that promised a full investigation but generally put the blame on protesters, calling them “members of extremist-minded groups.” At least 300 were injured.