Istanbul (AFP) - Turkish police detained Istanbul’s powerful mayor, Ekrem Imamoglu, Wednesday over two investigations into graft and “supporting terror”, prompting outrage from the main opposition CHP which slammed it as a politically-motivated “coup”.

Imamoglu is President Recep Tayyip Erdogan’s main political rival and his detention came just days before the CHP was expected to name him their candidate for the 2028 presidential race.

Widely seen as the strongest challenger to Erdogan – whose route to the presidency also included four years as Istanbul mayor – Imamoglu has been targeted by a growing number of what critics say are spurious legal investigations.

Hundreds of police joined the pre-dawn raid on his home, Imamoglu said on X before being taken away, with the authorities then briefly blocking access to social networks.

There was a heavy police presence on the streets, with hundreds fanning out around City Hall and closing off Taksim Square. And the governor banned all protests for four days.

“What has happened is an attempted coup,” railed CHP leader Ozgur Ozel in a speech at City Hall.

“Ekrem Imamoglu’s freedom to be a candidate is not being taken away, it is this nation’s freedom to elect him that is being taken away.”

His words were echoed by the mayor’s wife, Dr Dilek Kaya İmamoglu.

“This is a targeted political operation aimed at eliminating Turkey’s future president. This is a direct blow to the nation, and we will fight,” she vowed.

- Anger on the streets -

There was also anger on the streets.

“We’re living in a dictatorship!” said a shopkeeper called Kuzey.

“Whenever this guy and his dirty team see someone strong, they panic and do something illegal,” he said, referring to Erdogan and the AKP who have been in power since 2003.

“In the past, it was soldiers who carried out coups. Today it’s the politicians,” sighed 63-year-old Hasan Yildiz.

Despite the protest ban, 300 people rallied outside the police station where the mayor was taken, yelling: “Imamoglu, you are not alone!” and “Government resign!”

Nearby, police fired teargas to disperse 400 students protesting outside Istanbul University over its decision to revoke Imamoglu’s degree, an AFP correspondent said.

The move against Imamoglu sparked chaos on the country’s financial markets, with the lira falling 14.5 percent against the dollar, and the benchmark BIST 100 closing 8.72 percent lower.

“Today’s dip in the markets shows investors are concerned the arrest was politically motivated,” said Hamish Kinnear, a senior analyst with Verisk Maplecroft.

- ‘Nothing short of a coup’ -

Justice Minister Yilmaz Tunc said Imamoglu was being investigated for the “alleged crime of aiding and abetting a terrorist organisation” – namely the banned Kurdish PKK militant group.

A second investigation, involving 100 suspects, was focused on allegations of “bribery, extortion, corruption, aggravated fraud, and illegally obtaining personal data for profit as part of a criminal organisation”.

More than 80 people were rounded up early on Wednesday with some 20 others still sought – most were from the CHP.

The authorities have regularly targeted journalists, lawyers and elected political representatives, notably since the failed 2016 coup.

But the crackdown has intensified in recent months, with the authorities removing more than a dozen opposition mayors and taking action against any perceived opponents to stifle dissent.

“What happened this morning was nothing short of a coup against the main opposition party, with far-reaching consequences for Turkey’s political trajectory,” political scientist Berk Esen at Istanbul’s Sabanci University told AFP.

- Amnesty: ‘A massive escalation’ -

In a statement, Amnesty International said it was “a massive escalation in the authorities’ ongoing crackdown on peaceful dissent” and targeting of the opposition.

“While the weaponisation of vague anti-terrorism allegations to detain and prosecute opponents is not new, these latest detentions… represent an alarming intensification of the targeting of real or perceived critics,” it said.

Between October and March, the authorities jailed three CHP mayors in the Istanbul area. They also removed 10 mayors from the pro-Kurdish DEM party, with most replaced by government-appointed trustees.

Imamoglu was one of three more CHP mayors detained on Wednesday in a move that did not go unnoticed abroad.

EU chief Ursula von der Leyen said it was “deeply concerning” and Berlin denounced it as a “serious setback for democracy”.

- ‘Nipping his candidacy in the bud’ -

The raid occurred just hours after Istanbul University revoked Imamoglu’s degree, amid claims it was falsely obtained – a high stakes move as presidential candidates need a higher education qualification.

It also came just days ahead of a key CHP meeting at which the party was to have named him their candidate for the 2028 presidential race.

“I think it was about Erdogan nipping Imamoglu’s candidacy in the bud before his formal announcement as the opposition’s presidential candidate,” Soner Cagaptay, senior fellow at the Washington Institute for Near East Policy told AFP.

The 53-year-old, who was resoundingly re-elected as mayor of Turkey’s largest city and economic powerhouse last year, has been named in several legal probes, with three new cases opened this year alone.