At least 10 people sought medical assistance after a group of pro-Russian separatists attacked a rally in support of Ukrainian unity in the city of Donetsk, Monday.

Masked people armed with baseball bats, chains and stones attacked participants in an antifascist march in Donetsk, chanting nationalistic slogans along with it, Itar-Tass reports.

More than one thousand people took part in the march for support of a Single Ukraine. According to media reports, the United States moved to impose more sanctions against Russia over the crisis in Ukraine. Russia's Deputy Foreign Minister Sergei Ryabkov claimed that such measures are a distortion of foreign policy rather than a responsible approach to the situation, the Interfax news agency reports.

Meanwhile, masked and armed militants have seized a council building in another city in eastern Ukraine - Kostiantynivka, Monday.
The city is located just 160 kilometers from the Russian border, and 35 kilometers south of Slaviansk which has been in insurgents' hands for more than three weeks now.

On Monday, Donetsk Region Governor Serhiy Taruta and Donetsk Mayor Alexander Lukyachenko have proposed holding a nationwide referendum on broader powers for regions and on the status of the Russian language on 25 May.

According to Lukyachenko, such a referendum would ease the tensions in southeastern Ukraine.