Istanbul's mayor Ekrem Imamoglu, a key rival of President Recep Tayyip Erdogan, has been arrested by Turkish police as part of an investigation into alleged corruption and terror links. The arrest comes days before Imamoglu is expected to be nominated as the presidential candidate for his party. Demonstrations have been banned and social media platforms have been restricted in an attempt to prevent protests. Critics argue that the crackdown is politically motivated, while government officials claim the arrests are not politically motivated and that the judiciary operates independently.