Turkiye Finans, the largest Islamic bank in Turkey, told regulators that its chief executive Derya Gurerk had resigned from his position on Friday, an unexpected move at a time of growing competition in the sector. Executive vice president Osman Celik would take over the role temporarily, the bank said in a regulatory filing without elaborating on the departure of Gurerk, who had served on the role since 2011. Turkiye Finans, in which Saudi Arabia’s National Commercial Bank is the largest shareholder, has a predominant focus on corporate banking and is one of four incumbent Islamic banks in the country.