A coalition of former ethnic Albanian leaders of a war of independence against Serbian troops in 1998-1999 is leading with a third of the vote in Kosovo's national election.
The Central Election Commission reported that the ex-rebels' coalition came in first with around 35% of the vote. With 91% of votes counted, the nationalist Movement for Self-determination had about 27%, a point ahead of the coalition led by former Prime Minister Isa Mustafa.
No group can govern alone and a coalition is likely.
Final results for the new 120-seat parliament are expected later in the week. Twenty seats in parliament are reserved for ethnic Serbs and other minorities.
Ramush Haradinaj, 48, the leading coalition's nominee to be prime minister, told supporters at a midnight rally in Pristina that "we know that there is a lot of work ahead of us. But we are going to achieve them together".
The Movement for Self-determination also celebrated the results, which saw the party double its share of the vote. The party has been a disruptive force by releasing tear gas in the previous parliament, and its supporters threw firebombs outside it to protest the contentious deals with Montenegro and Serbia.
The party has nominated its former leader, 42-year-old Albin Kurti, as a candidate for prime minister.
Serbian President Aleksandar Vucic said the victory of hard-liners in Kosovo elections will create "a lot of difficulties and problems," but added that the European Union-mediated dialogue with Kosovo must continue.
He said the winners in the Kosovo election are "the same group that most openly threatened Serbs, and that will create a lot of problems".
The Serbian leaders consider Haradinaj a war criminal and have failed to get him extradited earlier this year from France where he was detained on a Serbian arrest warrant.
Serbia does not recognise Kosovo's 2008 declaration of independence.
Any winning cabinet will face a number of thorny issues like approving the border demarcation deal with Montenegro. Brussels insists Kosovo's parliament must first approve a border demarcation deal signed with Montenegro in 2015 as a condition for adding Kosovo to western Balkan countries whose citizens do not need visas to enter the EU's Schengen zone.
A further issue is the prospect of former ethnic Albanian senior rebel commanders facing prosecution in the newly established war crimes court. The court in The Hague is expected to shortly issue indictments for crimes committed against civilians during and after the 1998-1999 war with Serbia.