Iran's highest legislative body is set to hold an extraordinary session with Mir Hossein Mousavi and two other candidates who are questioning the election victory of President Mahmoud Ahmadinejad.
The Guardian Council meeting due on Saturday morning follows demands by Mousavi and Mehdi Karoubi for the June 12 poll to be annulled.
After days of marches by Mousavi supporters, further unrest is feared if protesters defy an order by the country's supreme leader to stop mass rallies.
Mohsen Rezaie, a conservative candidate, is also expected to join the council session to discuss 646 complaints over the election.
Abbasali Kadkhodai, a council spokesman, said: "We are urging candidates to avoid any remarks which can disturb public opinion until the Guardian Council carries out its final investigation."
The contested result gave Ahmadinejad a tally of about 63 per cent, to Mousavi's 34 per cent. The council has so far promised only to recount some ballots if irregularities are found.
Alireza Ronaghi, Al Jazeera's correspondent in the capital, Tehran, said that it was likely that the meeting would bring only minor changes to the poll outcome.
"I think the Guardian Council intends to review all of the complaints," he said.
"In some of those cases, there are some obvious irregularities and I am sure that they will be addressed. I'm sure some of the ballot boxes will be annulled and they will be deducted from the results.
"But ... I find it very unlikely that there will be major change in the final result."
The scheduled meeting comes a day after Ayatollah Ali Khamenei, Iran's supreme leader, backed Ahmadinejad's victory and cautioned that mass protests - which continued daily from the release of the poll results until Thursday - must cease.
That leaves Mousavi to decide on leading further protests, with the prospect of a violent crackdown by security forces, or complying with Khamenei's orders and accepting his election defeat.
It remains unclear whether a planned protest in central Tehran at about 4pm (11:30GMT) on Saturday will go ahead.
One Karoubi aide said that the demonstration "has not been cancelled and accordingly it must be held this afternoon."
Yet, Agence French-Press reported that the rally organisers would not go ahead with their plans after not receiving state permission.
On Friday, a Mousavi ally said he would not call on his supporters to demonstrate.
"Mousavi has no plans to hold a rally tomorrow or the day after tomorrow," he said.
However, his supporters protested last Tuesday despite Mousavi requesting that they refrain from doing so.
Ronaghi reported: "One of the main reformist cleric formations, the Association of Combatant Clerics, has been asking for permission to hold a rally nationwide on Saturday.
"But apparently some of their members have come out and said that the supreme leader's comments are the final call and whatever he says must be obeyed.
"So at the moment, no one knows. The thing is the people who hold the rallies have not been the best followers in listening to Mousavi on whether to go out or not.
"It is up to the people as to whether they will go out or not."
Television crews are prevented from filming rallies and many non-Iranian journalists have been prohibited from working in the country.
An indication that resistance to the results will continue came before dawn in Tehran on Saturday.
The opposition calls of "Death to the dictator" and "God is the greatest" were heard from the rooftops.
Khamenei said in a sermon during Friday prayers at Tehran University that if the supporters of defeated candidates fail to halt the protests "they will be responsible for its consequences, and consequences of any chaos".
He asserted that any complaints concerning the election would be investigated through legal channels but supported Ahmadinejad's "absolute and definitive victory" saying that the people "have identified the person they wanted".
"The Islamic establishment will never manipulate people's votes and commit treason ... the legal structures and electoral regulations of this country do not allow vote rigging," he said in his first public address on the issue since the election.
The speech was a rare public address by Khamenei, who usually speaks in public only at the end of Ramadan and the anniversary of the Iranian revolution, which brought the theocracy to power.
Khamenei called for calm following days of protests over the election results.
|Mousavi, right, has been ignored before when calling on his supporters not to protest [AFP]
"When you have peace of mind and soul you can decide wisely... Today our society is in need of peace and tranquility," he said.
During the speech, Khamenei accused Western powers and foreign media of attempting to undermine the elections and Iran's theocratic power structure by defining the dispute as between inside and outside the establishment, which he denied.
Khamenei instead equated the 85 per cent turnout in the poll with the legitimacy of the ruling system.
Khamenei has the final say in all of Iran's affairs under the constitution, and thus has the authority to annul elections and establish new polls.
Iran has been in a state of political unrest since Ahmadinejad was declared the winner.
Hundreds of thousands of Iranians have held street protests since the poll were announced with at least seven protesters being shot dead.
Hundreds of people have also been arrested, according to some unofficial Iranian Internet news sites.
Amnesty International, a UK-based human rights group, said on Friday that it believed 15 people had been killed as the protests have spilled over into violence, compared with just seven deaths reported on Iranian state radio.