Croatia's top court said on Friday that Zoran Milanovic, the country's president, who had campaigned to become prime minister ahead of this week's parliamentary election, could not head the new government.

"The president has been warned in time that he cannot participate in the campaign, but that he must (first) resign. Now it is over. He can no longer be a prime minister-designate," Constitutional Court President Miroslav Separovic told a press conference.

Croatia voted in a parliamentary election on Wednesday in which the ruling conservative HDZ party won most of the seats, but not enough to form a government alone.