Scores of pro-Russian demonstrators have stormed government buildings in Ukraine's eastern city of Donetsk.
Crowds of at least 5,000 protesters marched through the city's Lenin Square chanting "referendum, referendum", before breaking into the local headquarters of Ukraine's security services and the prosecutor's office, demanding the release of their self-appointed "governor".
Two men reportedly climbed on top of the entrance of the security headquarters and tore down the Ukrainian flag, replacing it with a Russian flag emblazoned with the words "Donetsk Republic".
Witnesses posted images of burnt books and a smashed-up van on social media, and several people, including at least one policeman, were wounded as demonstrators clashed with riot police.
The Interfax-Ukraine news agency reported that a Ukrainian Greek priest may have been seized by pro-Russian forces. The priest reportedly phoned his church authorities saying his flat was being stormed by police and pro-Russian "self-defence" forces.
Earlier this week, violence erupted between pro-Kiev and pro-Moscow demonstrators in Donetsk, leaving one person dead and at least 10 injured.
On Saturday, two people were killed and six injured in clashes between protesters in the Russian-speaking eastern city of Kharkiv.
Tensions are rising in Russia's Crimea region as the population votes in a referendum on whether to re-join Russia.
Election official Mykhaylo Malyshev said a record 44.27% of people had turned out to vote after the first six hours of voting. Crimea's pro-Russian Prime Minister Sergey Aksyonov put the latest turnout figure at 73.4%.
The vast majority of voters are expected to support secession from Ukraine, although the region's Tartar Muslims have boycotted the vote.
The EU and the US condemned the referendum as illegal, with EU leaders saying they plan to meet on Monday to discuss a new round of sanctions against Russia.
However, Russian President Vladimir Putin told German Chancellor Angela Merkel that the referendum is "legal" and "in full compliance with international law".