In a message to the president-elect Pezeshkian, Ashtiani wished him success in his mission.
Pezeshkian received more than 16 million votes against former nuclear negotiator Saeed Jalili with more than 13 million out of over 30 million votes cast, electoral authorities said.
"By gaining a majority of the votes cast on Friday, Pezeshkian has become Iran's next president," the interior ministry said.
The runoff on Friday followed a June 28 ballot in a snap election to find a successor to President Ebrahim Raeisi who lost his life with his foreign minister Hossein Amir-Abdollahian and others in a helicopter crash in northwest Iran.
Pezeshkian originally ran against a field of five candidates last week, winning the largest number of votes but falling short of a majority which sent him and Jalili to a second round.
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