Turkish police have detained the strongest rival to President Recep Tayyip Erdogan, a move that experts say is aimed at removing all possible contenders ahead of the next presidential election and further stretching his rule.

Authorities in Turkey have arrested dozens of people for "provocative" social media posts, after detaining the mayor of Istanbul Ekrem Imamoglu on Wednesday. Imamoglu was one of more than 100 people held on charges including corruption and aiding terrorist groups - a move that has sparked protests in Istanbul and the capital Ankara.

Critics say the arrest of Istanbul's mayor is part of a mounting crackdown by Turkey's president to silence all dissent.