At least 50 young men, many in balaclavas, have attacked the former office of the Party of Regions in Ukraine's eastern city of Kharkiv.
The office is currently used by Ukrainian lawmaker Mykhaylo Dobkin, who represents the Opposition Bloc in parliament.
The attackers destroyed a minibus parked near the office and smashed the building's windows with stones on August 3.
The attackers said they were representing the Ukrainian right-wing nationalist group Right Sector and an organization called Public Guard.
They said they gathered at the site to protest against the Opposition Bloc's participation in local elections in October and attacked the building after Dobkin's people started shooting at them with firearms, wounding one activist.
Kharkiv, Ukraine's second-largest city, is only about 20 kilometers from the Russian border.