The resignations of Borissov and the country's chief prosecutor have been the key demands of month-long street protests across the Balkan country. The mostly young protesters accuse those in power of links to the mafia, refusing to fight corruption and reform the judiciary, and suppressing freedom of speech.
Borissov has been in power since 2009 and his third term is scheduled to end next March. In Sofia, protesters have permanently blocked several key road intersections, causing huge traffic jams. They have set up tents and say they intend to remain there until their demands are met.
Meanwhile, one of the protesters, who went on hunger strike five days ago, was taken to hospital on Wednesday in critical condition.