Four organizers and instigators of a mass brawl in Donetsk, which led to casualties have been detained, Ukrainian Interior Minister Arsen Avakov has said.

"The first four of the organizers and instigators of the mass brawl after rallies in Donetsk, which led to casualties, were identified and detained during the night. Investigative actions are being conducted. Based on the first materials of the overnight investigation, these detentions are only the beginning. We will not apply the liberal rhetoric of influence on thugs with knives – there will be a tough personal response," he wrote on his page on Facebook on Friday morning.

Avakov said that an internal investigation aimed at assessing the actions of police officers during the events was also being conducted.

As reported, an activist and former spokesman for the Donetsk regional branch of the Svoboda Party, Dmytro Cherniavsky, died from stab wounds on March 13 after pro-Russian activists attacked participants in a rally "For a United Ukraine." The media also reported two or three deaths and at least 50 injuries, but these reports have not been officially confirmed.