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.

A university has invalidated Istanbul Mayor Ekrem Imamoglu's diploma in a move widely perceived as politically motivated.

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.