Georgia has launched a probe into the alleged “falsification” of its parliamentary elections, prosecutors said Wednesday, after the pro-Western opposition said the vote was “stolen” and Western countries criticized irregularities.

Pro-Western opposition parties refused to recognise the results of Saturday’s vote, which they claim was rigged in favor of the ruling Georgian Dream party.

U.S. President Joe Biden added his voice to international criticism of the election on Tuesday, saying he was “deeply alarmed” by democratic “backsliding” in the Caucasus country and that the vote was marred by “voter intimidation and coercion”.

“Georgian citizens have a right to peacefully express their views regarding the conduct of these elections, which independent international and domestic observers have not said were free and fair,” Mr. Biden said. “We call for all parties to strictly respect the rule of law and fundamental freedoms, which remain the foundation for Georgia’s Euro-Atlantic future.”

A statement by Georgia‘s prosecution service said it had “launched an investigation into the alleged falsification of the parliamentary elections.” The statement said President Salome Zurabishvili, who “is believed to possess evidence regarding possible falsification… has been summoned to the investigative agency for an interview” on Thursday.

Zurabishvili – at loggerheads with the ruling party – has declared the election results “illegitimate,” alleging election interference by a “Russian special operation,” a claim that was rejected by the Kremlin.

Opposition parties have said they would not enter the new “illegitimate” parliament and demanded “fresh” elections run by an “international election administration.”

Tens of thousands rallied in Tbilisi on Monday in protest, while the United States and European Union have condemned electoral “irregularities.”

A group of Georgia’s leading election monitors said they had uncovered evidence of complex, large-scale fraud. Near-complete election results showed the ruling Georgian Dream party won 53.9 percent, compared with 37.7 percent for an opposition coalition.