A Turkish court has issued a ruling that effectively removes the head of the country’s main opposition party, in the latest blow to challengers of President Recep Tayyip Erdoğan.

The ruling, issued by an appeals court in Ankara on Thursday, annulled a 2023 leadership contest within the Republican People’s party (CHP), deposing the party’s leader, Özgür Özel.

Özel, 51, has become the face of Turkey’s opposition, seen as responsible for the rejuvenation of the CHP as well as being one of few remaining figures from within the party who has avoided charges that could land him in detention.

The court ordered that Özel be replaced by his predecessor, Kemal Kılıçdaroğlu, who lost a pivotal general election to Erdoğan in 2023 despite a groundswell of opposition to the Turkish president’s two decades in power.

Özel’s election as party leader pre-empted Turkish local elections in 2024 where the CHP swept Erdoğan’s Justice and Development party (AKP) from power in municipalities and mayoralties across the country.

Earlier this week, another Ankara court ordered Özel to pay the president 300,000 lira (£4,900) in damages due to his remarks about Erdoğan, which include calling him an “oppressor”. Özel also gave a speech calling on Erdoğan to “leash your dogs”, in a criticism of a sweeping crackdown on Turkey’s opposition.

In response, Erdoğan called Turkey’s main opposition leader “delusional”, saying: “We have to protect the reputation of politics in the face of attacks.” Erdoğan has frequently lashed out at the CHP in public, accusing the party of a series of accusations including acting as “puppet of terrorists seeking to undermine this state”.

The court case that ultimately unseated Özel was widely criticised as an effort to subdue Turkey’s largest opposition party and reinstall a leader who is more amenable to Erdoğan’s rule. Kılıçdaroğlu, who has called for the “purification” of his own party, was sanguine in his response to the ruling when speaking to the pro-government channel TGRT Haber, saying he hoped it would prove “beneficial to Turkey and the CHP”.

The ruling jolted Turkey’s struggling economy amid fears of further instability: trading was briefly suspended on the stock market in Istanbul amid a sharp 6% drop after the CHP ruling.

Since the 2024 elections, observers have denounced a fresh crackdown targeting opponents of Erdoğan’s rule, primarily opposition mayors and local officials from the CHP. More than 20 CHP mayors have been detained in a wave of corruption, bribery and terrorism-related charges that has unseated mayors and municipal officials from towns and cities across the country and landed many in detention.

The arrest of Istanbul mayor and likely CHP presidential candidate Ekrem İmamoğlu last year represented a watershed for the party and for the country’s beleaguered opposition. Thousands took to the streets of Istanbul to protest against the detention of Erdoğan’s primary challenger, who once ruled the largest city in the country.

İmamoğlu has spent the intervening year in a maximum security facility near Istanbul. Earlier this year he was among 400 defendants who took the stand in a mass trial, all accused of taking part in a sprawling corruption scheme allegedly tied to his office as mayor.

Human Rights Watch called the trial part of a broad effort to weaponise the criminal justice system against the CHP.

Many other CHP municipal officials across Turkey have been accused of graft charges similar to the accusations against İmamoğlu: five officials from the Beşiktaş municipality were taken into custody as part of a bribery investigation earlier this week.

CHP officials have indicated they are keen to fight a presidential election expected next year, amid speculation that they could seek to run the jailed former mayor as a candidate.

Özel told the Guardian in an interview last year that the party had prepared plans for İmamoğlu to be the candidate even if he remained in detention, adding that he was prepared for the Turkish authorities to seek his arrest if Erdoğan “can’t cope politically like what happened with İmamoğlu”.

The upcoming election, he said, represented a referendum on whether there would be “autocracy or democracy in Turkey”.