Il Nuovo Postiglione - Thousands protest for second night over Istanbul mayor's arrest

The powerful and popular Imamoglu -- who is President Recep Tayyip Erdogan's main political rival -- was detained before dawn on Wednesday, just days before he was to be named as the candidate of his opposition CHP party for the 2028 presidential election.

Imamoglu has urged the nation and the judiciary branch to take a stand against what his party described as a political "coup."

As thousands gathered under tight security on Thursday, a handful of students tried to cross the barriers, prompting scuffles with police who fired rubber bullets, according to an AFP correspondent at the scene.

A second correspondent said police had "used rubber bullets and a lot of tear gas".

It was not immediately clear whether anyone was hurt.

Ozgur Ozel, leader of the main opposition CHP party, warned the police not to provoke demonstrators by firing tear gas or rubber bullets.

"If that happens, the Istanbul police will be held accountable," he warned from the podium.

It was the second night that thousands had defied a protest ban to gather outside City Hall to express their anger at Imamoglu's detention.

"Mayor Ekrem is not involved in corruption, nor terror. He's not a thief nor a terrorist," Ozel said, warning Erdogan that the protests would not stop.

"I didn't fill this square and these streets. You did. They are full because of you," he said.

- 'Tayyip resign!' -

"Tayyip, resign!" yelled the crowd of several thousand people, many of them university students, in a pointed message to the Turkish leader.

Elsewhere in the city, protesters banged pots and pans in several areas, including the upmarket Nisantasi district where cars honked their horns in solidarity, another AFP correspondent said.

After spending his first night in custody, Imamoglu called on the nation and the judiciary to take a stand against the government's move to silence dissent in a message on X passed through his lawyers.

"We as a nation must stand against this evil," he said, urging judges and prosecutors to "stand up and take action against those who are ruining the judiciary".

"You cannot and must not remain silent," wrote the 53-year-old.

The CHP has angrily denounced his arrest as a political "coup", with Ozel saying Imamoglu's only crime was "taking the lead in opinion polls".

- 'This is not a one-day protest' -

"The detention is illegal, it aims to block Imamoglu from becoming president, it seeks to stifle opponents," 24-year-old Basak Cohce, a student at Galatasaray University, told AFP.

"This is not a one-day protest, we will defend our rights until the end," she said as the crowd swelled outside City Hall.

"We are here on the streets to make our voice heard, young people like me will not remain silent," agreed a 19-year-old student from Istanbul Technical University called Yavuz.

Taksim Square and Gezi Park, both renowned for mass public protests over a decade ago, remained fenced off, and social media and internet access was largely restricted for a second day.

The arrest sent Turkey's financial markets into a tailspin, dealing a heavy blow to the Turkish lira.

Turkey's Central Bank said it would draw on its foreign exchange reserves if needed to prevent further harm to the currency, with economists saying it had already done so on Wednesday.

- Weaponising the justice system -

More than 80 people were rounded up in Wednesday's raids and investigators began quizzing them early on Thursday, local media said.

Already named in a growing list of legal probes, Imamoglu -- who was resoundingly re-elected last year -- has been accused of "aiding and abetting a terrorist organisation" -- namely the banned Kurdish militant group PKK.

He is also under investigation for "bribery, extortion, corruption, aggravated fraud, and illegally obtaining personal data for profit as part of a criminal organisation" along with 99 other suspects.

Interior Minister Ali Yerlikaya also said 37 people had been detained for posting content online that was deemed "provocative" and more investigations were under way.

By law, Erdogan -- who has been president for more than a decade, having been premier for 11 years before that -- cannot run again in the 2028 race.

But he wants to change the constitution to allow that, a move that requires opposition support, which analysts said could be complicated by Imamoglu's arrest.

A.Mariconda--INP