Mr Imamoglu faces two years and seven months in jail. The government’s move to ban him from politics has united opposition against Mr Erdogan, sparking protests in Istanbul.
Mr Erdogan’s remarks follow comments by the US and German governments condemning the charges against the mayor, with Germany calling it a “harsh blow against democracy”.
Mr Imamoglu was elected as mayor of Istanbul in 2019 with 4.1 million votes, defeating a rival from Mr Erdoagan’s Justice and Development (AKP) party by a small margin. The election result was annulled by the country’s Supreme Electoral Council, a decision critics of the government said was made under political pressure. A new election was held and Mr Imamoglu won by a much larger margin, of 800,000 votes.
The charges against him stem from this period — he allegedly called the Supreme Electoral Council “fools” following the annulment of the first 2019 mayoral contest result, but it is not clear why the charge of insulting public officials has only just been levelled against him.
"What is behind the storm sparked by a verdict these past few days? This debate has nothing to do with us — neither with me nor with our nation," Mr Erdogan insisted, in his first comments on the subject since Wednesday's verdict.
Several tens of thousands of people demonstrated their backing on Thursday in Istanbul for Mr Imamoglu, who established his credentials as an opposition figure with the heft to break Mr Erdogan's two-decade domination of Turkish politics after his mayoral success.
Mr Erdogan announced in June that he will stand again next year but a six-party-strong opposition alliance has yet to designate a joint candidate.
"What does it matter to us who the opposition candidate will be," Mr Erdogan pondered rhetorically, as he urged the opposition to have "the courage" to select its candidate.