Iran's supreme leader said Tuesday it is a "religious duty" for people to vote in this week's general election and strengthen the Islamic republic against the "propaganda" of its enemies.

"Participating in elections and voting... is a religious duty, not just a national or revolutionary duty," Ayatollah Ali Khamenei said in a speech, parts of which were aired on state television.

"Elections nullify many of the vicious plots the Americans have in their minds and Zionists have in their hearts against the country," he said, referring to US ally Israel.

Iranians are set to elect a new parliament on Friday, with conservatives expected to make a resurgence.

Observers expect a low turnout as many reformist and moderate candidates have been barred from running by the Guardian Council.

The council, made up of six clerics appointed by the supreme leader and six lawyers selected by the judiciary, disqualified more than half of the 14,444 hopefuls.

The move threatens the thin majority of President Hassan Rouhani's alliance in parliament.

Friday's election comes after months of domestic turmoil and steeply escalating tensions between Iran and its arch enemy the United States.

Iranian women queue to vote in the 2017 presidential election in the Shiite holy city of Qom
Iranian women queue to vote in the 2017 presidential election in the Shiite holy city of Qom AFP / Ali SHAIGAN

In November, nationwide demonstrations over petrol price hikes turned violent before being crushed in a deadly crackdown.

Tensions with Washington have risen since 2018 when US President Donald Trump withdrew from a landmark nuclear agreement and reimposed crippling sanctions.

But they have never come as close to a direct confrontation as in the past seven months, when it has happened twice, most recently after the US killed prominent Iranian general Qasem Soleimani on January 3.

Iran hit back on January 8 by firing a barrage of missiles at US troops in Iraq.

It had been on high alert for US retaliation that day when they shot down a Ukrainian airliner in Tehran, killing all 176 people on board.

The downing of the Boeing 737, which the armed forces later admitted was accidental, sparked more protests that turned political.

Khamenei said the election would show that Iran's enemies had failed to divide the nation.

"Watch how the people favour the election despite the enemies' insistence on distancing the people from the system," the supreme leader said.

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