Turkey launched a probe into the leader of the main opposition party for insulting President Recep Tayyip Erdoğan in the latest phase of a crackdown that has stoked investor fears about political instability and the government’s economic programme.

Turkey has arrested three more opposition mayors early as part of an investigation into alleged graft, officials from the main opposition Republican People’s Party (CHP) said, denouncing the arrests as a politically motivated crackdown.