A Turkish court on Wednesday sentenced Istanbul's popular opposition mayor Ekrem Imamoglu to nearly three years in jail in a politically charged trial that effectively bars him from standing in next year's presidential election.

Imamoglu's team immediately vowed to appeal against his conviction in a case stemming from a remark he made after defeating President Recep Tayyip Erdogan's ally in a hugely controversial 2019 mayoral vote.

People who are sentenced to less than four years are rarely put behind bars in Turkey. But Imamoglu's conviction for defamation disqualifies him from politics for the duration of the sentence.

He will continue serving as Istanbul Mayor while his appeal makes its way through the courts.

"This is a pathetic approach to democracy and the rule of law," Imamoglu's lawyer Kemal Polat told AFP.

The trial focused on an offhand remark Imamoglu made to reporters a few months after defeating Erdogan's ally in a re-run election held after his first victory was annulled.

Officials reported discovering hundreds of thousands of "suspicious votes" after Erdogan refused to acknowledge Imamoglu's initial win in a city that he himself ran before entering national politics two decades ago.

The decision backfired badly on Erdogan's party. Waves of protests and huge support from all political corners delivered Imamoglu an overwhelming victory in a re-run vote held that June.

Imamoglu let his frustration at the entire episode spill over a few months later by calling the people who annulled the first vote "idiots".

An Istanbul court sentenced Imamoglu to two years and seven-and-a-half months in prison on the charge of "insulting" public officials.

It also applied a separate clause of the penal code that bars the Mayor from politics.

The Istanbul Mayor is among a handful of opposition leaders that polls show could beat Erdogan in a head-to-head race in next June's presidential vote.

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