Ebrahim Raisi, ultra-conservative judiciary chief, set to win Iran's presidential election - CNN

However, experts said his election was unlikely to affect the course of indirect negotiations with the United States on reviving the 2015 nuclear deal.

Foreign Minister Javad Zarif said Saturday he expected that talks on returning to the terms of the deal would "most likely" conclude before the end of Rouhani's term in August.

"The Vienna talks are going well and it's likely that there will be an agreement before the month of August, but there are still obstacles," Zarif said.

If talks spill over into Raisi's tenure, they will largely rely on who the incoming president appoints as his foreign minister.

In 2015, the success of the deal, which saw Iran place limits on its uranium enrichment program in exchange for sanctions relief, was largely attributed to Zarif.

But experts say Iran is unlikely to engage with the West beyond returning to the nuclear deal, satisfying itself with bolstering relations with Russia and China.