Istanbul police have opened 32 investigations following allegations of voting "irregularities" made by the ruling party of President Recep Tayyip Erdogan after its shock loss in local elections, Turkish media reported Thursday.
More than 100 election officials have been summoned as part of the inquiries across three districts in Turkey's biggest city, according to state news agency Anadolu.
Mr Erdogan's Justice and Development Party (AKP) saw losses in Ankara and Istanbul – which the party or its predecessors had held since 1994 – in the elections of March 31, despite remaining the most popular party nationwide.
It has accused election officials of suppressing votes for their candidates and discounting valid ballots. The move comes as Mr Erdogan's ruling party presses ahead with efforts to have the March 31 Istanbul election results annulled over the alleged irregularities and for the vote there to be repeated.
The AKP has made an "extraordinary appeal" for a re-run of the election in Istanbul, which was won by a coalition of opposition parties headed by Ekrem Imamoglu. He has accused Erdogan's party of being "bad losers".
The country's electoral council is due to convene on Monday to discuss the appeal.
Several partial recounts in Ankara and Istanbul have so far supported the initial results, which saw Imamoglu win the Istanbul mayorship by less than 15,000 in a city of more than 15 million.
While the Istanbul appeal drags on, the rare defeat has prompted questions within the party over campaign strategy. Although the alliance helped them win a majority of votes nationwide, AKP officials say it has delivered limited benefits.
Mr Erdogan vowed on Saturday to confront opponents inside his own party weeks after the shock election defeats.
"While we're fighting outside, I have to say, we had people doing us wrong from the inside too," Mr Erdogan said during a speech at an AK Party retreat, without naming any individuals.
"What is going on in which province, in which district, all that information come to us. We know it all ... For the future of this organisation, we will call them to account. We're not going to carry them on our backs."
The president did not spell out what actions he would take. Authorities have suspended or sacked 150,000 civil servants and military personnel in recent years, accusing many of them of being involved in a failed 2016 military coup.
He has maintained that a conspiracy has taken place in Istanbul.
"Until the last moment, we will continue our legal struggle. It is certain that there is a scam here. We have to get the case resolved, so that we can find peace," he said.
"Although we have won the districts, we will question why we lost the big cities," he added. "We need to focus on what to do and how to evaluate this process, especially in metropolitan cities."