The pro-European Union, centre-right GERB party has won parliamentary elections in Bulgaria, exit polls suggest.
It is predicted to take around 32% of the vote, ahead of the Socialists with 28%.
Former Prime Minister Boyko Borisov, who leads GERB, said the party had the "duty to form a government".
Official results are expected on Monday but Socialist Party leader Kornelia Ninova has already conceded victory.
Sunday's election was the third in four years.
Mr Borisov, 57, resigned as prime minister after his party lost the November 2016 presidential election.
A caretaker administration took over after parliament was dissolved in January and will remain in place until a new government is formed.
Mr Borisov said GERB would endeavour to form a government quickly with coalition partners.
The Socialists have ruled out being part of any power-sharing agreement with GERB.
Bulgaria joined the European Union in 2007 and is one of its poorest member states. It is also a member of Nato.
The Socialists had pledged to improve ties with Russia if they were elected.