Turkey's top election body ordered a re-run of Istanbul's mayoral election on Monday after the party of President Recep Tayyip Erdogan complained about its shock defeat in the vote, the state news agency reported.
The ruling Justice and Development Party (AKP) narrowly lost Turkey's biggest city in the 31 March local elections, ending the party and its predecessors' 25-year control of the metropolis.
It claims there were "irregularities and corruption" that required a re-run of the mayoral election, which was won by Ekrem Imamoglu of the main opposition Republican People's Party (CHP) by just 13,000 votes.
Supporters of Ekrem Imamoglu cheer as they wait for him during a protest against the rerun of elections in Istanbul. Source: EPA
Mr Imamoglu said he would wait for an official declaration by the election body before reacting.
"There is no need to be in despair," he said in a message on social media.
The soft-spoken former district mayor had vowed to heal political divisions and reach across party lines.
But his victory - which was confirmed after two weeks of recounts in April - sent shockwaves through the ruling party.
Mr Erdogan, himself a former mayor of the city, once said winning Istanbul was like winning the entire country.
Along with the ruling party's defeat in the capital Ankara, it marked a rare electoral setback for Erdogan and reflected widespread concern over the deteriorating economy.
Istanbul, with 16 million residents, is Turkey's economic engine and controls a major chunk of public spending.
The CHP, which had previously called Mr Erdogan a "bad loser", said it was holding an emergency meeting after the election body's announcement.
The party's deputy chair, Onursal Adiguzel, who represents Istanbul in the national assembly, said the ruling was "neither democratic nor legitimate".
"Going to the polls against the AKP is allowed, but winning is forbidden ... This is downright dictatorship," he tweeted.
In a park in central Istanbul, supporters were gathering late Monday for a speech by Mr Imamoglu.
"I don't even know what to say. The lawlessness is so obvious," said one female supporter.
"If there is no rule of law ... they will trigger a civil war."
Turkey's President Recep Tayyip Erdogan speaks during a ceremony at presidential palace this week. Source: Pool Presidential Press Service
The defeated mayoral candidate, former prime minister Bilnari Yildirim, said he hoped the re-run would "be beneficial for our city".
Mr Erdogan presented the local elections as a matter of national survival, campaigning heavily even though he was not running himself.
For his supporters, Mr Erdogan remains the strong leader that Turkey needs as it faces internal and international security threats - while also speaking for religiously conservative Turks who have felt sidelined.
His critics say he has undermined the rule of law with a sweeping crackdown on dissent and sewn division by portraying his opponents as enemies of the state.
The AKP still won the most seats nationwide in the local elections, but it has been damaged by Turkey's first recession in a decade, as well as record-high inflation and a currency that has lost more than 12 per cent of its value against the dollar this year alone.
The party did not request a re-run of the election for the Istanbul local assembly, in which it won a majority of seats.