EDITORS’ NOTE: Reuters and other foreign media are subject  to Iranian restrictions on their ability to report, film or take  pictures in Tehran.

TEHRAN, (Reuters) – Iran’s supreme leader will  address the nation today for the first time since a disputed  election result triggered the biggest protests the Islamic  Republic has seen.

Ayatollah Ali Khamenei has urged Iranians to unite behind  hardline President Mahmoud Ahmadinejad but supporters of  defeated candidate Mirhossein Mousavi have so far ignored the  call, holding huge rallies in defiance of an official ban.

Khamenei’s speech at Friday prayers in the Iranian capital  follows a sixth day of protests by Mousavi supporters. On  Thursday, tens of thousands, wearing black and carrying candles,  marched to mourn those killed in earlier mass rallies.

The largest and most widespread demonstrations since the  1979 Islamic revolution have rocked the world’s fifth biggest  oil exporter, which is also caught up in a dispute with the West  over its nuclear programme.

Iranian state media has reported seven or eight people  killed in protests since the election results were published on  June 13. Scores of reformists have been arrested and authorities  have cracked down on both foreign and domestic media.

Iranian Nobel Peace Prize winner Shirin Ebadi said about 500  people had been arrested in the last week, and called for their  unconditional release. She said Iran should hold new elections  under the supervision of the United Nations.

Mousavi, a moderate who advocates better ties with the West,  has also called for the election to be annulled, saying pledges  by the country’s top legislative body, the Guardian Council, to  recount some disputed ballot boxes did not go far enough.

The council has invited Mousavi and two other defeated  candidates to talks on Saturday, and says it has begun “careful  examination” of 646 complaints.

Objections include a shortage of ballot papers, pressure on  voters to support a particular candidate, and the barring of  candidates’ representatives from polling stations.

Iran has denounced foreign criticism of the election,  although U.S. President Barack Obama’s administration has muted  its comments to keep the door open for possible dialogue.

At yesterday’s rally, protesters massed in a Tehran square,  responding to Mousavi’s call for people to gather in mosques or  at peaceful rallies to show solidarity with the victims and  their families.

They held photographs of those killed, some showing bloodied  faces, apparently taken after they died.

“Our martyred brothers we will take back your votes,” read  one placard. “Why did you kill our brothers?” said another.

Other banners told protesters to stay home today, when  Ahmadinejad supporters are expected to show their strength at  Khamenei’s Friday prayers, but to gather again the next day.

Mousavi supporters say he will be joined on Saturday by  reformist former president Mohammad Khatami and another defeated  candidate, liberal cleric Mehdi Karoubi.

Ahmadinejad has defended the legitimacy of the vote, telling  a cabinet meeting on Wednesday that 25 million of 40 million  voters had approved the way he was running the country.

The semi-official Fars news agency said two children of  powerful cleric Akbar Hashemi Rafsanjani, who backs Mousavi and  clashed with Ahmadinejad during campaigning, had been barred  from leaving Iran.

His daughter Faezeh addressed Mousavi supporters on Tuesday.  Hardline students called for her and her brother, Mehdi, to be  arrested.

Iran’s Intelligence Ministry said it had uncovered a  foreign-linked terrorist plot to plant bombs in mosques and  other crowded places in Tehran during the election.

State broadcaster IRIB quoted a ministry statement as saying  several terrorist groups had been discovered, adding they were  linked to Iran’s foreign enemies, including Israel.

Hamid Najafi, editor-in-chief of Kayhan International, an  English-language conservative Iranian daily, said the Guardian  Council investigation of the vote would calm unrest but the  overall result would not change because “there isn’t a millionth  chance of doing any fraud”.