Iceland's Pirate Party has tripled its seats in the 63-seat parliament, election results show.
It is in joint second place with the Left-Greens - with 10 seats each. But their centre-left coalition fell short of a majority to form a government.
The governing Progressive Party lost more than half of its seats in the poll triggered by the resignation of Prime Minister Sigmundur Gunnlaugsson.
Its junior partner, the Independence Party, has come top with 21 seats.
Prime Minister Sigmundur Gunnlaugsson stepped down in April in the wake of the leaked Panama Papers which revealed the offshore assets of high-profile figures.
Current Prime Minister Sigurdur Ingi Johannsson resigned on Sunday.
The anti-establishment Pirate Party, which was founded in 2012, had said it could be looking to form a coalition with three left-wing and centrist parties.
The Independence Party and the Pirates have ruled out working together, although correspondents say this could change as negotiations take place in the coming days.
Pirate Party founder and MP Birgitta Jonsdottir said she was "very satisfied" with the result.
"Our internal predictions showed 10 to 15%, so this is at the top of the range. We knew that we would never get 30%," Ms Jonsdottir told Reuters news agency.
The party won support from many in the wake of Iceland's 2008 financial crisis and the Panama Papers' revelations earlier this year.
It calls for more political transparency and accountability, free health care, closing tax loopholes and more protection of citizens' data.
Opponents, however, say the Pirate Party's lack of political experience could scare off investors and destabilise Iceland's recovering economy.