Ukraine's justice minister has warned anti-government protesters occupying her ministry she will call for a state of emergency if they do not leave.
Olena Lukash told local media she would ask the National Security and Defence Council to introduce the measures.
Protesters seized the building in Kiev late on Sunday and set up barricades outside with bags of snow.
Unrest is spreading across Ukraine, with activists taking over municipal buildings in several towns and cities.
Buildings have come under attack even in eastern areas, which have traditionally had closer ties with Russia and where President Viktor Yanukovych has enjoyed strong support.