Georgian President Salome Zurabishvili on Tuesday asked the country's constitutional court to annul last month's parliamentary election result, while police in Tbilisi cracked down on a protest against the vote, denounced by the pro-Western opposition as rigged.
The European Union and the United States have called for a probe into "irregularities" during the October 26 election won by the governing Georgian Dream party in the Caucasus country, which has candidate status for EU membership.
Pro-Western president Zurabishvili -- who is at loggerheads with Georgian Dream -- has called the vote illegitimate and accused Russia of interference, a claim Moscow has denied.
On Tuesday, she "filed a lawsuit at the Constitutional Court of Georgia, requesting the annulment of the election results as unconstitutional", her office said in a statement.
Zurabishvili wants the court to cancel the results "over widespread violations of voting universality and ballot secrecy", said Eka Beselia, the lawyer representing the president in the court.
Pro-Western opposition parties have refused to recognise the election result or enter the newly elected parliament, which they deem "illegitimate".
Zurabishvili has joined the opposition's calls for a new vote and has refused to issue a decree to convene the new parliament.
Prime Minister Irakli Kobakhidze, of Georgian Dream, has insisted the elections were free and fair and said parliament would convene Monday even without a presidential summons.
But a leading constitutional law expert, Vakhushti Menabde, said on social media Tuesday that the "new parliament can't convene until the constitutional court delivers its ruling on Zurabishvili's lawsuit".
The court has one month to deliver its judgement.
Since the vote, tens of thousands have taken to the streets in Tbilisi to protest against alleged electoral fraud.
Early Tuesday, police violently dispersed a sit-in protest outside Tbilisi State University where dozens of demonstrators had set up tents, blocking traffic on one of the main streets in the Georgian capital, an AFP photographer saw.
Massed police, some wearing masks, beat and forcefully dragged away journalists and protesters holding Georgian and EU flags.
Amid a heavy police presence, the rally continued into the afternoon, with hundreds of protesters blocking traffic in central Tbilisi.
The Interior Ministry reported that 16 people were arrested for "disobeying police", with three detainees later released.
The leader of the opposition Akhali party, Nika Gvaramia, said members of his party "have been detained and injured. Party activists have been beaten and arrested."
Ahead of the crackdown, the interior ministry urged protesters to disperse, saying "freedom of assembly and expression does not include the right to deliberately disrupt road traffic".
The opposition has announced a new mass rally for when the new legislature holds its first session.
EU foreign policy chief Josep Borrell said Monday that the bloc "will send a mission to Georgia... and the election will have to be investigated".
"The EU will never abandon you and your fight for EU values," he said in a statement after a meeting of the EU Foreign Affairs Council.
Critics have blamed the increasingly conservative Georgian Dream for derailing the country from its European path and bringing Tbilisi back into Moscow's orbit.
The party has denied the accusations.
Ahead of the elections, Brussels warned Tbilisi that the conduct of the vote would be decisive for its prospects of joining the bloc.
