Six people were injured by rubber bullets on Tuesday during a skirmish between different opposition groups at the Agriculture Ministry in Kiev, which was occupied last week by the Spilna Sprava, or Common Cause, radical group.
Protesters from the Euromaidan movement, reportedly armed, arrived at the ministry building on Vulitsya Khreshchatyk at around midday local time with the intention of convincing the Spilna Sprava members to leave.
Those arriving at the ministry said they had a deputative order to clear out occupied government buildings in exchange for the release of detained protesters, Argumenty i Fakty reported. The origin of the order is unclear.
But Spilna Sprava was unaware of the purported agreement and the "discussion" between the two opposition groups turned into a shootout in which "grenades flew" and first extinguishers were used, the report said.
Silna Sprava has since left the building, UNN news agency reported.
The six unidentified wounded people were later taken away in an ambulance, an eyewitness told Interfax.
Kiev police said they had not yet received information about the incident.
Spilna Sprava earlier seized the Energy Ministry building and a Justice Ministry building in Kiev, but both have been vacated over the last few days.
The Ukrainian parliament was set to debate the possibility of an amnesty for detained protesters on Wednesday.
On Tuesday, a skirmish took place in the Lviv region's administrative building between the activists who had seized it and members of nationalist group Svoboda, who were trying to remove them.