A Turkish court jailed Istanbul Mayor Ekrem Imamoglu pending trial on Sunday, local media reported, as more than 300 people were arrested during protests.
Turkish prosecutors requested his formal arrest during the day. A popular figure, Mr Imamoglu was arrested on Wednesday over alleged corruption and aiding terrorist groups. Several other prominent figures, including two district mayors, were also held.
Mr Imamoglu was questioned on Saturday for nearly five hours as part of an investigation into allegations of aiding the outlawed Kurdistan Workers’ Party (PKK), the Cumhuriyet newspaper reported.
A day earlier he was questioned for four hours over the corruption accusations. Mr Imamoglu rejected all charges during both interrogations.
"My dear nation, never be sad, never lose hope. We will, hand in hand, uproot this blow, this black stain on our democracy," Mr Imamoglu said on X, shortly after his arrest and called on Turkish citizens to head to the ballot boxes and vote.
"I invite my 86 million citizens to run to the ballot box and announce their struggle for democracy and justice to the entire world," he said.
"I stand tall, I will never bow," he said on X.
His arrest has led to debate on whether the move is politically driven in an attempt to remove him from the next presidential race, currently scheduled for 2028.
Government officials reject the accusation and say Turkey’s courts are independent.
The move has caused widespread protests across Turkey, with demonstrators rallying in several cities to voice their opposition.
Interior Minister, Ali Yerlikaya, said 323 people were detained following protests on Saturday night against Mr Imamoglu's detention.
Mr Yerlikaya said “there will be no tolerance for those who seek to violate societal order, threaten the people’s peace and security, and pursue chaos and provocation”.
Protests against the mayor's arrest have been growing since Wednesday, with the leader of the CHP calling on supporters to take to the streets for peaceful demonstrations directly against a five-day ban on protests from Turkish authorities in capital Ankara as well as Istanbul and Izmir.
They have been peaceful, however, a group of protesters, trying to break through barricades to reach Istanbul’s main square, threw flares, stones and other objects at police, which responded with pepper spray. Some demonstrators said rubber bullets were fired.
Police used water cannons and tear gas to scatter demonstrators in Ankara.
They are the largest protests since 2013, when Turkey was rocked by mass anti-government demonstrations that left eight people dead.
The Istanbul governor's office announced it was expanding a ban on demonstrations until March 26 and imposed restrictions on the entry and exit of vehicles deemed to be transporting people “likely to participate in unlawful activities”.