Bulgaria may hold snap parliamentary elections in spring amid the resignation of Prime Minister Boyko Borisov and his refusal to form a new government.
The center-right government formally resigned in November after the ruling party's candidate Tsetska Tsacheva was beaten by Rumen Radev in the presidential election.
"I will not propose to form a new government and I hand back the mandate," Borisov told outgoing President Rosen Plevneliev during a ceremony in the capital, Sofia, on Friday.
Under Bulgaria's constitution, the outgoing president will give another mandate on December 8 to the second largest party, the Socialist BSP, which has already declared it would reject such a mandate.
Plevneliev will then choose a third party in a final attempt to avoid snap elections.
Analyst Dimitar Ganev said, "The road to early elections is clear," describing Borisov's resignation as a "tactical move" aimed at keeping his party's leading position.
Plevneliev will have to appoint an interim administration, which would be the country's fifth government in less than four years, until Radev takes office in January.
A former Bulgarian air force commander, Radev, who is backed by the opposition Socialists, is expected to dissolve the current legislature and set a date for snap elections when he takes office on January 22.
Polls show that GERB is expected to win most seats in the parliament but falls short of the majority needed to govern alone.