Ukrainian House, a major conference centre near Independence Square, was a flashpoint in Ukraine’s power struggle on Saturday night.
Used as a base for riot police in Kyiv, it was stormed by protesters, who broke windows and threw Molotov cocktails.
Officers resisted with stun grenades and water hose but demonstrators persisted, forcing police to leave.
The protest movement already holds other key buildings in the capital and regional government headquarters outside Kyiv.
Denouncing presidential concessions, one protester told euronews: “You can’t buy Ukrainian people. We are not for sale. We take decisions and we want Yanukovych and the government to step down.”
“We have reached a point where police can use violence at any time to clear the place,” another man said. “The only thing they understand is force.”
It is two months since the movement began but unrest has intensified over recent days with the introduction of sweeping anti-protest laws, pushed through parliament by presidential loyalists.
The opposition claims at least six activists have been killed.
Our correspondent in Kyiv, Maria Korenyuk, said: “The presidential proposition is interesting for opposition leaders, but they have called on protesters to stay on the streets of Kyiv and on the barricades until Tuesday, January 28. That is when parliament will hold a special session to discuss the controversial laws that put restrictions on protesters.”