A large crowd of pro-Russian separatists has stormed the regional administration's headquarters in the eastern Ukrainian city of Luhansk.
A few dozen men, some reportedly armed with metal bars, smashed windows and doors to break into the building.
Activists shouting "Referendum Russia" later flew a Russian flag over it.
Earlier, Russia criticised sanctions imposed by the US and EU on individuals and companies over their alleged actions aimed at destabilising Ukraine.
Deputy Foreign Minister Sergei Ryabkov said the US had "essentially lowered an 'Iron Curtain'" by targeting Russia's high-tech sector.
The EU, he added, had proved that it was "under Washington's thumb". READ MORE