Protesters in Istanbul marched through Kadikoy to call for President Recep Tayyip Erdogan’s resignation following the passage of the April 16 constitutional referendum, which will expand executive powers of the Turkish president.

Additional protests were reported in Istanbul’s Besiktas District, as well as in the southeastern Izmir province, where scuffles with riot police have reportedly taken place.

Opposition parties had voiced concerns over allegations of fraud and vote tampering. Both the Republican People’s Party (CHP), who plan on contesting at least 2.5 million votes, and the pro-Kurdish Peoples’ Democratic Party (HDP) said it would object to two-thirds of ballots cast due to vote “manipulation”.