The eight candidates running for president are to stage a televised debate on Friday, with the ailing economy topping the agenda, as Iran's spiritual guide Ayatollah Ali Khamenei called for a clean vote.
Campaigning for the June 14 presidential poll officially kicked off last week after Iran's electoral watchdog, the Guardians Council, approved the eight -- including several figures close to Khamenei -- from a field of nearly 700 would-be candidates.
Two main contenders were disqualified.
The campaign has so far been mostly confined to short provincial tours and appearances on state television and radio, rather than the lively street rallies by supporters of candidates in the 2009 presidential election that gave Mahmoud Ahmadinejad a second four-year term.
The Guardians Council has barred moderate ex-president Akbar Hashemi Rafsanjani and Ahmadinejad's close ally Esfandiar Rahim Mashaie.
The debate on Friday, the first of three, is expected to take the form of a Q&A session, with Iran's ailing and sanctions-hit economy expected to top the agenda.
Plunging oil exports combined with foreign currency curbs have triggered a severe economic crisis, with inflation officially running at more than 30 percent and foreign investments drying up.
The run-up to the 2009 election, which led to anti-regime protests over voter fraud charges, produced heated exchanges between Ahmadinejad and his pro-reform opponents, Mir Hossein Mousavi and Mehdi Karroubi, in live face-to-face debates on state television.
On Wednesday, Khamenei warned the candidates against creating tensions.
"The candidates should refrain from tarnishing their opponents and the realities of the society just to attract votes," he told a group of lawmakers in remarks reported on his website.
This year's campaign has been low-key. Street rallies are banned, according to security officials, and candidates have yet to roll out election posters or banners, even in major cities.
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"I have not yet received many orders to print posters or banners for the presidential election," said Ali, 32, owner of a major printing house in the northeastern city of Mashhad.
"This is probably because there are so many of them. Many will withdraw and do not want to waste their money."
The eight candidates comprise five conservatives, including top nuclear negotiator Saeed Jalili, two moderates and a reformist.
Pre-recorded messages from candidates began to air on Saturday and have already roused controversy.
Mohsen Rezai, former commander of the elite Revolutionary Guards and a conservative, had his speech censored as he spoke of a father who had lost three sons in the 1980s war against Iraq.
Quoting the unnamed man, Rezai criticised raging inflation and high unemployment in the country, saying the father had threatened to commit suicide if the economy was not fixed.
Rezai's controversial comments on "ethnic discrimination" were also edited out, media reports said.
The debate on Friday, which could run up to four hours, is expected to provide a glimpse into candidates' plans for the economy, which has been hit hard by international sanctions targeting Iran's vital oil income over Tehran's nuclear ambitions.
Although the nuclear case is a uniting factor among all candidates, who defend Iran's "legitimate right" to have a peaceful atomic programme, their tactics to resolve a years-long standoff with the West could differ.
Boasting his non-compromising stance in nuclear talks with world powers, Jalili has vowed to implement a "resistance economy" in response to sanctions imposed over Tehran's nuclear ambitions that have led to raging inflation and high unemployment.
Hassan Rowhani, the only cleric in the race, says his experience in leading talks with the so-called P5+1 group -- the United States, Russia, China, France, Britain plus Germany -- could help resolve the nuclear standoff.
All key decisions in the Islamic republic, including the nuclear programme, rest with Khamenei.
Former foreign minister Ali Akbar Velayati, another conservative close to Khamenei, has pledged to curb inflation of more than 30 percent "in 100 days," and to ease Iran's international isolation under Ahmadinejad.