Turkey’s electoral body has been criticised for ordering Istanbul’s local elections to be re-held after the ruling AK Party lost the city in March.
The AKP claimed there were “irregularities and corruption” behind the opposition CHP’s tight victory.
But the CHP’s winning mayoral candidate, Ekrem Imamoglu, called the decision “treacherous”.
The re-vote will be held on Sunday 23 June.
Monday’s announcement sparked protests across the city, with hundreds of residents gathering in several districts of Istanbul shouting anti-government slogans.
The European Parliament has also condemned the re-run of the election, stating that it would terminate the credibility of the democratic process in Turkey.
Why the re-run?
Recep Ozel, who is an AKP representative on the electoral board, said the re-run was ordered because some result papers had not been signed and some electoral officials were not civil servants.
However, the chairman of the CHP, Onursal Adiguzel, said the re-run showed it was “illegal to win against the AK Party”.
Mr Adiguzel took to Twitter to bemoan that the decision was “plain dictatorship”.
He wrote: “This system that overrules the will of the people and disregards the law is neither democratic, nor legitimate.”
In a speech aired on social media, Mr Imamoglu slammed the electoral board, saying they were influenced by AKP.
He told the crowd: “We will never compromise on our principles…This country is filled with 82 million patriots who will fight… until the last moment for democracy.”
Local elections took place in Turkey on Sunday 31 March, and were seen as a referendum on President Recep Tayyip Erdogan’s leadership amid a sharp economic decline.
Although an AKP-led alliance won 51% of the national vote, the secularist CHP claimed significant victories in the capital Ankara, Izmir and Istanbul – where President Erdogan had formerly been the mayor.
More than 8 million votes were cast in Istanbul and Mr Imamoglu was declared the winner by a margin of less than 14,000 in April.
The AKP has since challenged the results in Istanbul and Ankara, which has led to opposition accusations that they are trying to illegally win the election.
President Erdogan’s own party is split on the issue, with diehard loyalists believing that victory was stolen, while other elements have accepted the loss and argued that rejecting the outcome would be seriously damaging to Turkish democracy.