Widely seen as the only politician who could defeat Erdogan at the ballot box, Imamoglu has been jailed on corruption accusations he vehemently denies and is also being investigated in a terror probe.

His arrest has sparked days of protests that have spread from Istanbul across the country in Turkey's worst unrest in over a decade.

US-based Human Rights Watch said Monday that Imamoglu's arrest was the latest example of a judicial system "weaponised to remove a leading opposition politician from the political scene", adding the Erdogan administration "has a well-established track record of incarcerating people for political purpose."

Here is a list of the main political figures behind bars in Turkey:

- Osman Kavala -

A leading critic of Erdogan, 67-year-old philanthropist and activist Osman Kavala has been in prison since he was arrested in 2017.

He is serving life without parole after being convicted of attempting to overthrow the government and financing the 2013 Istanbul Gezi Park protests.

Initially sparked by plans to raze an Istanbul park, the demonstrations morphed into a wider protest movement that spread across the country, rocking Erdogan's government when he was prime minister.

In 2019, the Strasbourg-based European Court of Human Rights (ECHR) said the arrest of the Paris-born businessman sought to silence him and deter other human rights defenders.

The violations in the case "pursued an ulterior purpose... namely that of reducing Mr Kavala, and with him all human rights defenders, to silence," the ECHR ruled.

However Turkey, which as a Council of Europe member is obliged to implement ECHR rulings, refused to release him.

An appeal court upheld his conviction in 2022, along with the 18-year sentences handed to seven other defendants, including urban planner Tayfun Kahraman, a top former official at Istanbul City Hall.

- Selahattin Demirtas -

Selahattin Demirtas, 51, former presidential candidate and figurehead of Turkey's then-main pro-Kurdish HDP party, was arrested in 2016 with the country still in the throes of a crackdown in the wake of the failed coup against Erdogan.

In jail ever since, he was sentenced last year to 42 years for his alleged role in a series of deadly protests that erupted in 2014.

Until the rise of Imamoglu, Demirtas was seen as the only politician in Turkey who could rival Erdogan's rhetorical skills and was known to some admirers as "Kurt Obama" (Kurdish Obama) after the then-US president.

There had been some speculation in recent months that Demirtas could be released as Erdogan seeks to restore peace to the Kurdish-dominated southeast but this has yet to materialise.

As in Kavala's case, Turkey ignored an ECHR ruling ordered his release. His detention was aimed at "stifling pluralism and limiting freedom of political debate", the court ruled in 2018.

- Imamoglu allies -

The mayors of two Istanbul districts, Sisli district mayor Resul Emrah Sahan and Beylikduzu mayor Mehmet Murat Calik, have both been detained in the same case against Imamoglu and ousted from their positions.

Also jailed is Mahir Polat, a key aide to Imamoglu and an expert in cultural heritage, who had been leading the mayor's cultural and architectural projects in the city.

- Journalists, academics, a judge -

Erdogan's critics are fighting a years-long crackdown on the freedom of expression and media independence in Turkey.

The offence of "insulting the president" has been frequently used during Erdogan's last term to muffle dissident voices.

Media watchdog Reporters Without Borders (RSF) ranks Turkey in 158th place out of 180 countries in its press freedom table.

Dozens have fled abroad, including the former chief editor of the Cumhuriyet daily, Can Dundar, convicted in absentia to more than 27 years in prison in 2020 for a report on Turkish weapons deliveries to armed jihadist groups in Syria.

More than a thousand university academics were also targeted in the purge of institutions that followed the 2016 coup attempt.

One was former UN court judge Aydin Sefa Akay, a former Turkish diplomat, who was jailed on charges of links to the coup.