Istanbul Mayor Ekrem Imamoglu, who's Turkey's biggest rival to President Recep Tayyip Erdogan, has appeared in court for the first time since he was arrested last month and placed in a high-security jail.

Turkey's main opposition leader on Sunday pledged further protests against the jailing of Mayor Ekrem Imamoglu, President Tayyip Erdogan's chief rival, aiming to sustain Turkey's biggest demonstrations in more than a decade.

Istanbul’s jailed mayor, Ekrem Imamoglu, is due to appear in court in multiple cases separate to his arrest last month, increasing the pressure on the opposition figure seen as the main challenger to Turkish President Recep Tayyip Erdogan.