Constitutional Court says Zoran Milanovic cannot take up PM post because he did not first step down as president.

“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 said at a news conference on Friday.

“Everyone is obliged to adhere to the constitution and the law,” he added.

Croatia held parliamentary elections on Wednesday, in which the ruling conservative Croatian Democratic Union (HDZ) won the most seats but not enough to form a government alone.

The vote was held after a bitter campaign between longtime political foes – the conservative incumbent, Prime Minister Andrej Plenkovic, and the left-wing populist Milanovic.

For months, Plenkovic and his Croatian Democratic Union (HDZ) party seemed poised for an easy victory that would secure his third term as premier.

But in mid-March, Milanovic, who tops opinion polls, made the shock announcement that he would challenge Plenkovic and become the candidate for the Social Democrats.

Milanovic dissolved parliament on March 18, triggering this week’s snap election in the European Union member state of 3.8 million people. He said he would run for prime minister and resign only after winning the polls.

The Constitutional Court then immediately warned him that he could only stand in the elections if he first stepped down as president.

But Milanovic ignored the warning and campaigned across the country, accusing Plenkovic of leading the “most corrupt government in Croatia’s history”.

Corruption has long been the Achilles heel of the HDZ, which has been in power most of the time since Croatia’s 1991 independence from Yugoslavia.

The HDZ won 61 seats in the 151-member assembly, and a centre-left coalition led by the Social Democratic Party (SPD) won 42. The nationalist, right-wing Homeland Movement party came third with 14 seats, making it a likely kingmaker.

‘Preparation for coup d’etat’

Al Jazeera’s Marina Barukcic, reporting from Zagreb, said President Milanovic’s next move was unclear after the court’s verdict.

“He believes that the Constitutional Court’s decision is a preparation for a coup d’etat led by Prime Minister Andrej Milanovic,” she said.

Barukcic said the president promised to bring back the will of the people to the state.

Plenkovic said on Thursday that it would be known “very soon” with whom the party would form a new parliamentary majority.

The SDP was also trying to cobble together a majority although its task appears more difficult.

Croatia has a parliamentary democracy in which the prime minister and his cabinet set all major policies. The president nominates the prime minister based on election results, may dissolve parliament and acts as the head of the armed forces with some say in foreign policy.

Final election results are not expected until next week because a rerun is needed in two polling stations after irregularities were recorded.