Opposition leaders said the Supreme Electoral Board's decision to invalidate the results from Istanbul's election raises concerns about President Recep Tayyip Erdogan's grip on power and Turkish democracy in general.
A top aide for Erdogan told The Associated Press that the voiding of the mayoral election in Turkey's biggest city amounts to "a victory for Turkish democracy" by ensuring the results reflect the voters' choice.
Ekrem Imamoglu of the opposition Republican People's Party placed first by a slim margin in the March 31 mayoral election, defeating the ruling party candidate, former Prime Minister Binali Yildirim. Erdogan's conservative and Islamic-based Justice and Development Party then charged that a series of election irregularities made the results illegitimate.
Turkey's state-run Anadolu Agency said the Supreme Electoral Board revoked Imamoglu's mandate and called a new election for June 23. As grounds to annul the March 31 results, the board said that some ballot station heads were not civil servants as required by law, the news agency said.
Yildirim, the loser in the election, said he hoped the decision would lead to "beneficial and beautiful results for Istanbul."
In a statement to the AP, presidential communications director Fahrettin Altun said: "Having held free and fair elections for nearly seven decades, Turkey will complete this process in a transparent, lawful and orderly manner."
Leaders of the Imamoglu's main opposition party held an emergency meeting in the capital of Ankara late Monday.
Addressing thousands of his supporters in Istanbul, Imamoglu accused the electoral board of bowing to pressure and threats from Erdogan's party. He vowed to use "democracy" to win back the "rights" that he said were taken away by force. The crowd called for the electoral board members to resign and accused Erdogan of stealing the vote.
Kati Piri, the European Parliament's rapporteur on Turkey, said on Twitter: "This ends the credibility of democratic transition of power through elections in Turkey."
Police set up barricades around the electoral board's headquarters in Turkey's capital, but there were no immediate signs of major demonstrations. Protesters banged pots and pans in several Istanbul neighborhoods, the opposition Birgun newspaper reported.
Howard Eissenstat, a Turkey expert at the nonprofit Project for Middle East Democracy and a Middle East history scholar at St. Lawrence University in New York, said Monday's ruling "removes the last fig leaf of competitive elections" hiding the erosion of democracy in Turkey.
"Turkey wasn't democratic yesterday and it's not democratic today," Eissenstat said.
He noted that Erdogan's party previously invalidated election results in Turkey's mostly Kurdish-populated regions after a pro-Kurdish party won and replaced elected mayors with government appointees.
"Erdogan cannot afford to lose in the second round. It would a disastrous display of weakness," Eissenstat said.
The local elections held across Turkey on March 31 produced setbacks for the president. His party lost city hall in the capital as well as in Istanbul, ending 25 years of the Justice and Development Party and its Islamist predecessor governing both cities.
The loss of Istanbul, the country's commercial and cultural capital, was particularly hard for Erdogan. He began his political ascent as Istanbul's mayor.
At pre-election rallies, the president had repeatedly told crowds, "Whoever wins Istanbul, wins Turkey" and "Whoever loses Istanbul, loses Turkey."
Istanbul, with its 15 million residents and strategic location straddling Europe and Asia, accounted for 31% of Turkey's GDP of $851 billion in 2017 and draws millions of tourists.
The city government had a budget of $8.8 billion last year. The municipality has awarded lucrative contracts to businesses close to the government over the years and offers huge financial resources and employment opportunities.