Ukraine's justice minister has threatened to declare a state of emergency if protesters do not leave the justice ministry in Kyiv, which they seized late Sunday.
In a television appearance on Monday, Justice Minister Olena Lukash also warned that she would ask for talks between the opposition and President Viktor Yanukovych to be ended if the building is not returned to the government.
Opposition leaders have said Yanukovych's offer, to name protest leader Arseniy Yatsenyuk of the Fatherland Party prime minister and former boxing champion and leader of the UDAR party, Vitaly Klitschko, his deputy, is not enough to end the demonstrations, which are now spreading eastwards into parts of Ukraine considered to be in support of the president.
Yatsenyuk told a crowd that the opposition is "not afraid" of accepting more political responsibility, but Yanukovych still has to meet several demands. They include early elections, freedom for jailed protesters, and the repeal of anti-protest laws.
Marchers took to the streets in late November, after Yanukovych backed out of a trade deal with the European Union in favor of closer ties to Russia.