Voting was extended Friday in second round elections for almost a quarter of the seats in Iran's parliament, a crucial showdown between reformists and conservatives seeking to influence the country's future.
The polls will decide who has the most power when lawmakers are sworn in next month, opening or potentially closing a path to social and political change in the Islamic republic.
Tension over the vote's high stakes was underlined by a shooting involving supporters of rival candidates in a southern province, a security official said. The rare incident of political violence left four people wounded.
Iran's reformists -- who have encouraged foreign investment, support moves for greater diplomatic rapprochement and seek social reforms at home -- are allied with President Hassan Rouhani's government and made major gains in the first round on February 26.
That came just six weeks after Tehran's implementation of a nuclear deal with world powers lifted crippling economic sanctions long blamed for hobbling the economy.
Polling stations opened at 8:00 am (0330 GMT) for the second round which is taking place in 21 provinces, but not the capital Tehran, with 68 of 290 seats in parliament at stake.
Around 17 million citizens were eligible to vote in constituencies where no candidate won the minimum 25 percent required in the first round.
Voting had been scheduled to close at 1330 GMT but the interior ministry said polling stations would stay open two hours longer. No reason was given. Final results are expected on Sunday.
Mehdi Saadatmandi, who voted in Robat Karim, a city southwest of Tehran, said he came to the ballot box "to finish what was done in the first round".
"If the economy is fixed, the politics will be fixed also and if the parliament is in line with the government then things will move forward much better," the 50-year-old said, opting for the reformists.
Conservatives, including vocal opponents of the nuclear agreement which reined in Iran's atomic programme, lost dozens of MPs in the first round, suffering a wipeout in Tehran, where reformists took all 30 seats.
However Friday's voting -- the top two candidates from the first round are competing head to head -- covers 55 smaller towns and cities where conservative support held up.
"We should protect the country from the arrogant powers and their infiltration," said Zahra Karimdoost, a schoolteacher in Robat Karim who voted conservative, referring to the United States.
"They follow the leadership more seriously," she said, alluding to supreme leader Ayatollah Ali Khamenei and other clerics at the top of the establishment who have warned that rising foreign interest in Iran must not be accompanied by Western culture or social values.
Nationally, reformists won 95 seats and the conservatives 103 in February with nominally independent candidates and minorities sharing others, meaning no faction won a majority.
The outcome of the second round could change that.
Khamenei urged a strong turnout and has said Friday's voting is no less important than the first round.
Mohammad Reza Aref, a partly US-educated engineer and leader of the reformist pro-Rouhani List of Hope, has set a target of at least another 40 lawmakers.
Gains for the president's allies would make legislative reforms more likely.
However, if conservatives perform more strongly amid concern over the nuclear deal -- officials including Khamenei have complained that the United States is not honouring its commitments -- Rouhani's hopes for a more supportive parliament could founder.
Although the conservatives went backwards two months ago they have not changed tack, keeping up pressure over what they say is a silent agenda among reformists to give up the principles of the 1979 Islamic revolution.
"We hope that people in this round can have a parliament in line with the goals of Imam and the leadership by electing principlists," said Gholam-Ali Hadad Adel, head of the conservative coalition.
He was referring to revolutionary leader Ayatollah Ruhollah Khomeini and his successor Khamenei, Iran's ultimate authority with powers that far outweigh Rouhani, who was voted into office in a landslide in 2013.
Hadad Adel was a victim of the reformist surge in February, losing his own seat in Tehran.