While people in Istanbul reacted to the decision to re-run the city’s elections by pouring into the streets and banging pans and pots to make their voice heard, in Europe the highest charges also sounded worried.

Federica Mogherini, the EU’s foreign affairs chief, and Johannes Hahn, its enlargement commissioner, said in a joint statement: “The justification for this far-reaching decision, taken in a highly politicised context, should be made available for public scrutiny without delay.”

The two insisted: “Ensuring a free, fair and transparent election process is essential to any democracy and is at the heart of the European Union’s relations with Turkey.” 

They called on the government to allow international observers to monitor the rerun election.

Europe Rapporteur on Turkey, Kati Piri, said: "Erdogan does not accept defeat and goes against the will of the people. AKP pressured YSK to re-run local elections in Istanbul. This ends the credibility of democratic transition of power through elections in Turkey."

CHP's Ekrem Imamoglu, who was confirmed as Istanbul's mayor in April, called the decision "treacherous".

The new vote will be held on 23 June.

The CHP candidate for mayor of Istanbul, Ekrem Imamoglu, was elected with 48.80 percent of the votes, while the AKP candidate, Binali Yildirim, former speaker of the Turkish parliament, got 48.55 percent, some 13,000 votes less than his rival.