Iranians were voting for a new parliament, with turnout seen as a key measure of support for Iran’s leadership as sanctions weigh on the economy and isolate the country diplomatically.
The disqualification of more than 7,000 potential candidates, most of them reformists and moderates, raised the possibility of lower-than-usual turnout.
Iran’s leadership and state media urged voter participation, with some framing it as a religious duty.
Supreme Leader Ayatollah Ali Khamenei cast his ballot at a mosque near his Tehran office shortly after polls opened at 7am and urged Iranians to the polls.
“Anyone who cares about Iran’s national interests should participate in the election,” he said.
Earlier in the week, Mr Khamenei said high voter turnout will thwart “plots and plans” by Americans and supporters of Israel against Iran.
“Enemies want to see what the results of the US maximum pressure are,” he said, referring to US sanctions and pressure from Washington that have strangled Iran’s ability to sell its oil abroad, forcing its economy into recession.
On the eve of the vote, the Trump administration imposed sanctions on two senior officials of the Guardian Council, including its chief, and three members of its elections supervisory committee.
US officials said those targeted were responsible for silencing the voice of the Iranian people by rejecting more than 7,000 candidates.
Around 7,000 candidates left in the race after the disqualifications are running in 208 constituencies for the 290-seat chamber.
Tensions with the United States could strengthen hard-liners by reinforcing long-held distrust of the West.
The crisis with Washington spiked after a US airstrike in January killed Iran’s top general, Qassem Soleimani.
The strike led to a tense confrontation in which Iranian forces accidentally shot down a Ukrainian passenger plane after it took off from Tehran, killing all 176 people on board.
Most of those killed were Iranian.
The shoot-down, and attempts by officials to initially conceal the cause of the crash sparked public anger and protests in Iran.
The election is being held at a time of growing economic hardship.
Iranians have seen the price of basic goods skyrocket, inflation and unemployment rise and the local currency plummet since President Donald Trump withdrew the US from Iran’s nuclear agreement with world powers and imposed sanctions.
The economic woes faced by ordinary Iranians fuelled anti-government protests in November.
International human rights groups say at least 300 people were killed in the protests.
The parliament in Iran does not have power to dictate major policies, but it does debate the annual budget and the possible impeachment of ministers.
Power in Iran ultimately rests with Mr Khamenei, who has final say on all key matters.
Also looming over the election is the threat of the new Covid-19 virus, which has been confirmed in five people in Iran this week, including two elderly citizens who died in the city of Qom.
Concerns over the spread of the virus, which originated in central China, prompted authorities in Iran to close all schools and Shiite seminaries in Qom.