Turkey’s opposition issued a rallying call on Tuesday for voters to re-elect the ousted mayor of Istanbul after his victory was overturned by officials.
The Republican People's Party (CHP) ignored calls to boycott an election re-run, instead pledging to inflict a second defeat on President Recep Tayyip Erdogan’s party.
Imamoglu earned a narrow victory over Erdogan's candidate in the March 31 elections.
But the election board made the decision to hold a second vote after complaints from Erdogan's AK Party, who alleged irregularities.
The move was greeted with dismay overseas and raises questions about whether Erdogan, who has consolidated power throughout his 16 years as a political figurehead and is increasingly accused of authoritarianism.
The Turkish Lira fell sharply after the news, threatening to further destabilise the Turkish economy, which has entered a recession.
'Election board gangsters'
CHP leader Kemal Kilicdaroglu told a cheering crowd of supporters that he had a message for the “gangsters” on Turkey’s election board.
“Since you want another election so much, do whatever you want," he said. "We will emerge victorious [again] in this election."
Some demonstrators took to the streets of Istanbul late on Monday, while others banged pots and pans from their homes in a noisy protest.
Guy Verhofstadt, leader of the Alliance of Liberals and Democrats for Europe in the European Parliament, called the decision “outrageous” and said it “highlights how Erdogan’s Turkey is drifting towards a dictatorship".
He added: “Under such leadership, [EU] accession talks are impossible. Full support to the Turkish people protesting for their democratic rights and for a free and open Turkey!”
The ousted CHP mayor, Ekrem Imamoglu, gave an uplifting message to supporters that became a trending Twitter hashtag — #herşeyçokgüzelolacak — meaning “everything will be alright.”
Popstar Tarkan, who had 3.5 million followers, was among the celebrities using the hashtag.
"This has been a huge blow to democracy, " said Imamoglu. "We should repair and remedy this process."
The same candidates will contest the June 23 re-run, as Imamoglu will face the AK Party’s Binali Yıldırım. There was speculation in local media that minor candidates could stand aside to boost Imamoglu's chances of a second victory.
Commuters in Istanbul were divided on the news. "If there is any issue it should be re-run for things to be clear. I side with the re-run,” said local resident Sevim Filiz. The AK Party “is more effective, better, and has more services for the common people,” he added.
But Ziya Yalcin said: "An election was won. Then, from the same ballot box three types of votes are accepted yet a particular [mayoral candidate] type of vote was not accepted. From this point of view, it is a disgrace.”
Opposition newspaper Birgun also branded the election board decision as a "coup," adding "justice has been suspended" and "democracy has been cancelled."