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.

Protests that erupted across Turkey following the arrest of the main challenger to President Recep Tayyip Erdogan have taken a new direction with calls for a one-day shopping boycott.