Iranian President Hassan Rouhani has an unassailable lead in the country's presidential election, an Iranian official source said Saturday, citing an early unofficial tally, and is on course to defeat his hardline rival Ebrahim Raisi.

"It's over, Rouhani is the winner," the source said on condition of anonymity.

Rouhani had won 21.6 million votes, compared to 14 million for Raisi, with 37 million votes counted, the source added. There were about 4 million more votes still to be tallied, the source said.