The centre-left Coalition for Bulgaria led by the Bulgarian Socialist Party (BSP) turned down a mandate to form a cabinet, like its main rival GERB two days earlier.
Speaking at a joint news conference with President Rossen Plevneliev, BSP leader Sergei Stanishev also said he would not be a prime minister regardless of the results of the forthcoming elections, the Bulgarian National Radio reported.
On Thursday, Plevneliev will name the date when parliament will be dissolved and snap elections held. The head of state will hand a mandate to the third largest parliamentary group, the Movement for Rights and Freedoms, to form a government and if they decline, he will appoint a caretaker cabinet.