The Mayor of Istanbul has been detained as part of a Turkish corruption investigation – just days before he was due to be selected as a presidential candidate.

Ekrem Imamoglu, from the secular Republican People’s Party (CHP), is seen as one of Turkish President Recep Tayip Erdogan’s strongest political rivals.

Prosecutors say he is accused of being a “criminal organisation leader suspect”.

Authorities detained 100 suspects – including other politicians, journalists and businessmen – as part of the investigation, and the Istanbul governor’s office has imposed four days of restrictions in the city.

Imamoglu wrote on social media that “the will of the people cannot be silenced”.

In a video posted online, he vowed to “stand resolute” for the people of Turkey “and all who uphold democracy and justice worldwide”.

“I stand firm in my fight for the fundamental rights and freedoms,” Imamoglu added.

The arrest comes as part of a major crackdown on opposition figures nationwide in recent months.

Critics have condemned the moves as politically motivated. But Erdogan, in power for 22 years, and his party have denied the claims, insisting that Turkey’s judiciary is independent.

Last year, Imamoglu won a second term as Istanbul’s mayor, when his CHP party swept local elections there and in Ankara.

It was the first time since Erdogan came to power that his party was defeated across the country at the ballot box.

The elections were also a personal blow to the president, who grew up in and became mayor of Istanbul on his rise to power.

Dozens of police officers were involved in the early-morning raid on Imamoglu’s house in Turkey’s largest city.

The CHP’s presidential selection, in which Imamoglu is the only candidate, is set to take place on Sunday.

It came a day after Istanbul University annulled his degree due to alleged irregularities – a decision which, if upheld, would prevent him from running in presidential elections.

According to the Turkish constitution, presidents must have completed higher education to hold office.

Imamoglu called that move “legally baseless”, adding that universities “must remain independent, free from political interference, and dedicated to knowledge”.

His CHP party has characterised the recent interventions against him as a “coup attempt” to “prevent the nation from determining the next president”.

The party’s chairman, Ozgur Ozel, wrote on X that making decisions on behalf of the people, replacing their will, or using force to prevent it, amounted to a coup.

Its deputy chairman, Ilhan Uzgel, accused the government of using the detention as an “instrument to intimidate” Turkey’s opposition.

He told the BBC his party was “very concerned about the state of democracy in Turkey in general”.

Pro-government media outlets report that as well as being accused of extortion and fraud, Imamoglu is also alleged to have aided the PKK.

The PKK – or Kurdistan Workers’ Party – has waged an insurgency since 1984, and is proscribed as a terrorist group in Turkey, the EU, UK and US.

Following Wednesday’s mass detention, Istanbul’s governor ordered a four-day ban on all demonstrations, meetings and press releases in Istanbul, in order to preserve “public order” and stop “possible provocative actions”.

Many streets in Istanbul have also been closed to traffic, while some metro lines have also cancelled their services.

And reports suggest officials have severely restricted access to social media sites like X, YouTube, Instagram and TikTok after the arrests.

This is not the first time Imamoglu has faced legal issues.

In 2022, he was sentenced to more than two-and-a-half years in prison for insulting public officials in a speech.