First-round voting saw a turnout of 41 percent, marking the lowest since the 1979 Islamic Revolution. Candidates needed at least 20 percent of all valid votes in their constituency to be elected in the initial round.

Friday's vote was to fill the seats of 45 deputies, out of the 290 in parliament, in 15 of Iran's 31 provinces, including Tehran, officials said.

Supreme leader Ayatollah Ali Khamenei was among the first to cast a ballot as voting began.

"If God wishes, dear people, everyone should participate in these elections and vote. Greater participation signifies a stronger parliament," he said.

In March, 25 million Iranians took part, out of 61 million eligible voters.

The main coalition of reform parties, the Reform Front, had said ahead of the first round that it would not take part in "meaningless, non-competitive and ineffective elections".

The vote was the first since nationwide protests broke out following the September 2022 death in custody of Mahsa Amini, 22.

Amini, an Iranian Kurd, had been arrested for allegedly flouting the Islamic republic's strict dress code for women.

Interior Minister Ahmad Vahidi on Wednesday said participation in the second round was "as important" as the first.

"Those with influence among the people should encourage the nation to participate in it," he said, according to Mehr news agency.

In the 2016 parliamentary elections, first-round turnout was above 61 percent, before falling to 42.57 percent in 2020 when elections took place during the Covid pandemic.