"The Constitutional Court has established that with his statements and behaviour, the president has put himself in a position where he cannot be the prime minister-designate of the future government," the court's decision said. The conservative Croatian Democratic Union (HDZ) of Prime Minister Andrej Plenkovic won the most seats in parliament, 61, but not enough to govern alone. Although it came second with 42 seats, the centre-left Restart Coalition led by Milanovic's Social Democratic Party (SDP) is also trying to build a coalition in the 151-seat parliament. The far-right Homeland Movement emerged as a potential kingmaker after winning 14 seats. Milanovic made a surprise announcement that he would run for prime minister hours after calling the election. The Constitutional Court later warned him that he would first have to resign, a warning he ignored. The head of state has insisted that he did not breach Croatia's constitution by openly backing the opposition during the campaign and offering himself as their candidate for prime minister, accusing the current HDZ-led government of widespread corruption. He has also sharply criticised the judges of the Constitutional Court, calling them a "bunch of gangsters". The showdown between Croatia's two top politicians has dominated the vote, which is also seen as a test ahead of European Parliament elections in June. Milanovic, who has become a nationalist-populist Eurosceptic, has criticised the European Union's (EU) policies over the war in Ukraine. If he forms a government, such positions could potentially open the door to stronger pro-Russian influence in the country, similar to Hungary and Slovakia. The HDZ went into the election tainted by corruption scandals and even its traditional right-wing partners have ruled out joining it in a future government. Milanovic, for his part, has provoked outrage by only declaring himself as Plenkovic's challenger a month before the election and running a campaign as the HDZ's main critic while still head of state. Croatia is due to hold a presidential election later this year. Read Also: Polls give victory to PM's party in Croatian elections (in Portuguese)