Turkish authorities have detained the mayor of Istanbul, 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 Tayyip Erdogan’s strongest political rivals.

Prosecutors accused him of corruption and aiding a terrorist group, calling him a “criminal organisation leader suspect”.

Police detained 100 people – 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 said online “the will of the people cannot be silenced”.

In a social media video he said he filmed while police were outside his home, he vowed to “stand resolute” for the people of Turkey “and all who uphold democracy and justice worldwide”.

And in a handwritten note posted on his X account after his arrest, he said the people of Turkey would respond to “the lies, the conspiracies and the traps” against him.

Protests have erupted on Turkey’s streets and university campuses, and in underground stations, with crowds chanting anti-government slogans. It is a display of public anger not seen in years.

There were reports of clashes between protesters and police in Turkey’s largest city. Reuters news agency footage shows police using pepper spray pellets to disperse crowds outside Istanbul University.

The government has banned public gatherings in Istanbul as part of the four days of restrictions. But more protests are anticipated nationwide as opposition leaders, including Imamoglu’s wife, urge people to “raise their voices”.

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

UK-based internet watchdog Netblocks said on Wednesday Turkey had severely restricted access to social media sites like X, YouTube, Instagram and TikTok.

The arrest comes as part of a major crackdown nationwide in recent months, targeting opposition politicians, municipalities, journalists and figures in the entertainment industry.

Following the Istanbul mayor’s arrest, concerns over Turkey’s shift toward autocracy were expressed on social media, with some calling for an opposition boycott of the upcoming presidential elections, arguing that a fair and democratic vote is no longer possible.

Imamoglu’s party, the CHP, even condemned the arrests as “a coup against our next president”, a sentiment widely echoed by pro-opposition voices.

But Turkey’s justice minister criticised those who linked Erdogan to the arrests.

Yilmaz Tunc said it was “extremely dangerous and wrong” to suggest this was a political move, insisting that nobody was above the law in Turkey.

Erdogan and his party have also denied the claims, insisting that Turkey’s judiciary is independent. He has been in power for 22 years.

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 Istanbul.

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

Imamoglu’s arrest 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”.

Presidential elections are currently scheduled for 2028. Erdogan cannot currently run for office again, as he is in his second term and previously served as prime minister before that.

The only way Erdogan could contest another election would be to change the constitution, or call an early election before his term ends.

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.

Earlier this month the group announced its decision to lay down arms, following a call from its imprisoned leader, who had engaged in talks with Turkish officials.

International reaction to the arrest has been negative, with EU, French and German officials all condemning the arrests.

A Council of Europe statement said the detention of Imamoglu “bears all the hallmarks of the pressure on a political figure considered as one of the main candidates in forthcoming presidential elections.”

The Turkish lira, meanwhile, briefly crashed to an all-time low against the US dollar, as markets reacted poorly to the political uncertainty.

While many were shocked to wake up to the news of Imamoglu’s arrest, legal pressure on the popular opposition leader is far from new.

He has faced multiple investigations and was handed a political ban in December 2022 over allegations of insulting Turkey’s electoral board in 2019 – a verdict he appealed, with the final ruling still pending.

Additionally, he has been the subject of cases related to alleged tender irregularities during his tenure as mayor of Istanbul’s Beylikduzu district.

More recently, on 20 January, a new case was filed against him over his criticism of a prosecutor.