Iran will hold a runoff presidential election to replace the late hard-line President Ebrahim Raisi, an official said on Saturday, after an initial vote saw the top candidates not securing an outright win.

The election this Friday will see reformist candidate Masoud Pezeshkian facing off against hard-line former nuclear negotiator Saeed Jalili.

The results were announced during a news conference, broadcasted on Iranian state television by Mohsen Eslami, an election spokesman.

Pezeshkian took the lead receiving 10.4 million of the 24.5 million votes cast. While Jalili got 9.4 million, Parliament speaker Mohammad Bagher Qalibaf garnered 3.3 million, and Shiite cleric Mostafa Pourmohammadi secured over 206,000 votes.

In Iran, the law says that a candidate must secure over 50% of all votes cast to win. If that requirement is not met, the two top candidates will proceed to a runoff the following week.

Historically Iran has only had one runoff, in 2005, when hard-liner Mahmoud Ahmadinejad defeated former President Akbar Hashemi Rafsanjani.

However, once the new leader chosen the country's Guardian Council, an appointed and constitutionally mandated 12-member council, would need to formally approve the results, but according to Eslami there were no immediate challenges from any contenders.

The interior ministry reported the turnout was 40 percent which, if correct, makes it the lowest figure since the Islamic Revolution in 1979.

The figure is another indication that many Iranians remain disenchanted with the lack of democracy in their country, with women in particular suffering from a lack of basic freedoms.