Romania's top court annulled an ongoing presidential election after accusations of Russian meddling and said on Friday the entire process, which had been due to conclude this weekend, would have to be re-run.

The second round had been scheduled for Sunday and voting has already begun in polling stations abroad. It would have pitted Calin Georgescu, a far-right, pro-Russian candidate, against pro-European Union centrist leader Elena Lasconi.

"The electoral process to elect Romania's president will be fully re-run, and the government will set a new date and ... calendar for the necessary steps," the court said in a statement.

Georgescu scored single digit numbers in opinion polls before the first round vote on Nov. 24 but then surged to a first-place finish that raised questions over the result.

Georgescu wants to end Romanian support for Ukraine against Russia's invasion. If he won the presidency it would upend the pro-Western politics of the EU and NATO member, pushing Romania closer to a belt of states in central and eastern Europe that have powerful populist, Russia-friendly politicians, including Hungary, Slovakia and Austria.

Friday's court ruling plunged the country into institutional chaos. Current President Klaus Iohannis's term ends on Dec. 21 and it was unclear who would be head of state after this date.

Analysts said the ruling may erode institutions, trigger street protests and ultimately still endanger the nation's pro-Western course. It was not yet clear if Georgescu would be allowed to take part in the re-run election.

Romania's top security council declassified documents on Wednesday that said the country was a target of "aggressive hybrid Russian attacks" during the election period.

Russia has denied any interference in Romania's election campaigns.

The top court, which had validated the first presidential round on Monday, said in its Friday reversal that it was "seeking to ensure the fairness and legality of the electoral process", adding that a detailed explanation of its ruling would be released at a later date.

There was no immediate comment from Georgescu, but he was due to make a statement at 1900 GMT on Friday.

George Simion, the leader of the opposition hard-right Alliance for Uniting Romanians (AUR) called the court ruling a "coup d'etat", adding "nine politically appointed judges, scared that a candidate outside the system had all chances to become Romania's president, decided to annul Romanians' will".

Simion came fourth in the first round. He and AUR then endorsed Georgescu.

Lasconi condemned the court's ruling. "The constitutional court's decision is illegal, amoral and crushes the very essence of democracy, voting," she said.

However, Social Democrat Prime Minister Marcel Ciolacu supported the move, calling it "the only correct solution".