Both the United States and the European Union, which made good on pledges to slap punitive sanctions on Ukrainian officials deemed to be responsible for the deadly escalation, warned Mr. Yanukovych to avoid declaring a state of emergency, which could take the country deeper into civil conflict. But short of calling in troops, it looked unlikely that Mr. Yanukovych could restore his battered authority and regain control of the capital.

As the protesters, reinforced by swarms of ordinary residents, erected barricades around their extended protest zone, a woman mounted a stage to appeal for help from foreign governments to prevent the president from declaring a state of emergency.

“A state of emergency means the beginning of war,” she said. “We cannot let that happen.”

In the center of Kiev, however, war had basically broken out, with the police having been authorized to use live ammunition. Just after dawn, young men in ski masks opened a breach in the police barricade near the stage on Independence Square, ran across a hundred yards of smoldering debris from what had been called a protective ring of fire and confronted riot police officers who were firing at them with shotguns. Snipers also opened fire, but it was unclear which side they were on.

Sviatoslav Khanenko, a lawmaker and a head of the medical service of the National Resistance Headquarters, said by telephone that about 70 people had been killed and more than 1,000 had been wounded. Some news reports said 100 people had been killed.

The death tolls could not be corroborated. But even at the lower casualty numbers reported by Kiev’s municipal health authorities, Thursday was the most lethal day in Ukraine since independence from the Soviet Union more than 22 years ago.

By noon, 11 corpses had been laid out in a makeshift outdoor morgue under a Coca-Cola umbrella at the end of Independence Square. Other bodies were taken elsewhere.