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Turkey: A tie between candidates
Mr Erdogan, 69, who has been in charge of the country for 20 years, is seeking a third consecutive term as president, but Mr Kilicdaroglu has presented him with his toughest ever challenge.
Opinion polls before the election had given Mr Kilicdaroglu, who heads a six-party alliance, a slight lead, and two polls on Friday even showed him above the 50% threshold.
However, most had suggested a tight margin.
Turkey’s voters have also been electing parliamentarians to their 600-seat assembly.