"Raisi's main challenge will be the economy. Eruption of protests will be inevitable if he fails to heal the nation's economic pain," said a government official.
The vote Friday will choose a successor to Iran's moderate President Hassan Rouhani, who cannot run again now after serving two consecutive four-year terms, and who leaves office in August.
"We don't make any plans, we just live from day to day," said Mahnaz, a 30-year-old saleswoman in a Tehran beauty products shop, summing up the glum mood.
Rouhani said the audio was leaked just as the Vienna talks were "at the height of their success, so that it creates discord inside" the Islamic republic.