Protests in Ukraine appear to be spreading further outside the capital Kiev, with reports of unrest in 10 cities in other parts of the country.
Protesters besieged government buildings and in some cases clashed with police and government supporters.
Opposition leader Arseniy Yatsenyuk has rejected an offer by President Viktor Yanukovych to appoint him prime minister. He said key demands must be met, including new elections.
The president also suggested another opposition figure, former boxer Vitali Klitschko, take the post of deputy prime minister following talks on Saturday.
A BBC correspondent in Kiev says the opposition appears to have taken Mr Yanukovych's offer of concessions as a sign of weakness and is forging ahead with a campaign to unseat him.
The demonstrations began in November after Ukraine decided not to sign an accord on more co-operation with the EU and instead opted to deepen ties with Russia.
On Friday protesters seized a number of government buildings in Ukrainian cities outside Kiev: Chernivtsi, Ivano-Frankivsk, Lutsk and Lviv.
On Saturday the protests spread to cities further east, including Vinnytsya, south-west of Kiev.
The BBC says reports now suggest unrest is spreading further into the east, which traditionally has closer ties with Russia and is Mr Yanukovych's support base:
The opposition is demanding that a free trade agreement with the European Union be signed and political prisoners be freed, including former Prime Minister Yulia Tymoshenko.
They also demand the repeal of recently introduced laws restricting public protest, and early presidential elections. A vote is not due until 2015.