ISTANBUL (AP) — A Turkish court on Wednesday convicted Istanbul’s jailed opposition mayor and the chief rival to President Recep Tayyip Erdogan of insulting and threatening a public official and sentenced him to a year and eight months in prison.

Mayor Ekrem Imamoglu, who is being held in a prison west of Istanbul since March 23, is expected to appeal the verdict, which is part of several ongoing legal proceedings against him.

The case, which predates his arrest, stems from comments he made on Jan. 20 in which he criticized Istanbul Chief Public Prosecutor Akin Gurlek, accusing him of targeting opposition figures through alleged politically motivated investigations.

The court on Wednesday convicted Imamoglu of insulting and threatening Gurlek but acquitted him of the charge of publicly identifying him with the intent of making him a target.

Imamoglu, regarded as the main challenger to Erdogan's more than two-decade-rule, has denied the accusations.

The mayor was arrested alongside other politicians from the main opposition party as part of investigations into alleged corruption. His arrest triggered the largest street protests in Turkey in more than a decade.

Despite being behind bars, he was officially nominated as the presidential candidate of the main opposition Republican People’s Party, or CHP. Elections are due to be held in 2028, but may come sooner.

Since Imamoglu’s arrest, dozens of officials from CHP-controlled municipalities have faced waves of arrests as part of investigations into alleged tender rigging and bribery.

The arrests have drawn widespread criticism from opposition leaders, who argue that the charges are politically motivated. Imamoglu himself has described the trial as “punishment, not justice,” and accused the judiciary of acting under government pressure.

Erdogan’s government insists that the courts are impartial and free of political involvement.