Vitaly Klitschko, the former boxer turned Ukranian presidential hopeful, has been forced to cancel a rally in the eastern city of Donetsk, as pro-Russian protests in the city turned violent.
Across the eastern regions of the divided nation, efforts to stage "Ukrainian unity" rallies were crushed by an angry pro-Russia backlash. Supporters of Vladimir Putin, the Russian President, broke up a gathering in the Crimean city of Sevastopol beating up the crowd, as Cossack guard units used whips to thrash some of the activists.
Dozens of men chased and beat some of the 200 people who had gathered in Sevastopol to mark the 200th anniversary of the birth of Taras Shevchenko, the country's national poet.
Similar scenes broke out at the point where Klitschko's rally was due to take place in Donetsk, after a handful of defiant women turned up despite the cancellation of the event, to hold Ukraine's blue and yellow flag. They faced a baying crowd of thousands, waving imperial Russian flags and Soviet banners.
"Klitschko, go," they shouted.
Eventually, the women were forced to run for their lives as the mob broke through police lines, beating at least one woman before she was rescued by security officials.
"I am afraid there will be war," said Natalia Zadorozhuaya, a housewife. She admitted that she was relieved the Klitschko appearance had been cancelled. To have gone ahead would have been too provocative when their opponents were already on the march.
"I don't know how I am going to get out of here safely but if the pro-Ukraine side had gathered here in large numbers there would have been a real fight," she said. "I think we need help."
Klitschko had warned that Russia was sending provocateurs to Ukraine to stir up divisions in the east. Despite the strong local hostility to politicians from western Ukraine who spearheaded the revolution against President Viktor Yanukovych, Klitschko tried to show he could tap into a groundswell for keeping the country intact.
"Russia is using pure propaganda and trying to create division based on language. Tourists from Russia are here to stir up trouble," he said. "We in Ukraine have to show our unity."
The threat of violence was particularly marked in Crimea, the peninsula seized by Russian forces, where local leaders are arranging a referendum on joining Russia.
A group of young men wearing heavy boots and T-shirts emblazoned with USSR menaced the marchers in Simferopol, the capital of Crimea.
"We came to show we're here," said one of the men, Dima Yurteev. "To show that we're the majority."
Putin threw Russia's full weight behind the Crimean vote, even though it has been rejected by the interim Government in Kiev and the West. "Putin underlined in particular that the steps taken by Crimea's legitimate authorities are based on international law and aimed at guaranteeing the legitimate interests of the peninsula's population," a Kremlin statement said.
The statement emerged after Putin talked on the phone with British Prime Minister David Cameron and Angela Merkel, the German Chancellor. Downing St said Putin had promised to pursue a diplomatic outcome to the crisis.
Forces in Crimea were holding 30 Crimean border officials after taking over their post and had set a deadline for soldiers in Evapatoria to surrender.
A Ukrainian military spokesman said a further 200 vehicles had been seen coming ashore at Kerch in the east.