Protests erupt across Turkey after the detention of Istanbul mayor Ekrem Imamoglu, who is President Recep Tayyip Erdogan's main rival. Imamoglu denies corruption charges brought against him and thousands of people have taken to the streets in protest. More demonstrations are planned and tensions could rise as a court is expected to rule on Imamoglu's arrest. European leaders have criticized the detention as a sign of democratic backsliding in Turkey.