The Reformist Bloc has returned a mandate handed out by President Rosen Plevneliev to form a government, clearing the way for an early election this spring.
The Reformist Bloc is a loose alliance of centrist and right-wing parties and the junior partner in the outgoing Bulgarian government.
President Rosen Plevneliev had chosen the Reformist Bloc as a third party that could have tried to form a new cabinet without resorting to early elections, after Prime-Minister Boyko Borisov stepped down last month.
Bulgarian President-elect Rumen Radev declined the invitation of the sitting head of state, Rosen Plevneliev, to put forward his cabinet line-up before assuming office in January.
Radev's refusal means the cabinet in resignation, led by Prime Minister Boyko Borisov, will have to stay on until January 22, when the new President will appoint his interim government.
Political analysis by Plamen Asenov.