KIEV, March 14 -- Ukrainian Parliament speaker Alexandr Turchynov, the acting president, on Friday ordered an investigation into the death of a protester during clashes in the eastern city of Donetsk.

"We must immediately investigate the situation, detain those involved in the bloodshed and punish them for the crime in a legal way," Turchynov was quoted by his press office as saying.

Turchynov has expressed deep grief over the death of the 22-year-old pro-Kiev activist, who "staged his demonstration to support the integrity of Ukraine" and extended condolences to the man's family.

Meanwhile, Ukrainian Interior Minister Arsen Avakov said police had detained four people suspected of organizing the violent brawl in Donetsk, which led to the first death of a protester in the crisis-hit Ukraine since tensions moved from Kiev to southern and eastern regions.

The violent clashes between pro-Russia and pro-Ukrainian demonstrators in Donetsk on Thursday also left 26 people from both sides injured.

Local media reported three protesters had died.

Demonstrations in Ukraine began on Nov. 21, following a government decision to put on hold an association agreement with the European Union and opt for closer relations with Russia. So far, more than 100 people have been killed during the unrest.