TEHRAN, June 18 (RIA Novosti) - Iranian presidential challenger Mir Hossein Mousavi has called on his supporters to hold a day of mourning on Thursday for those killed in post-election protests.

Tehran has been swept by mass demonstrations over alleged ballot fraud in the landslide reelection of the hardline president, Mahmoud Ahmadinejad, on June 12. Eight people were shot dead on Monday during street protests.

On his website Mousavi asked supporters to wear black in respect of the victims.

"I ask the people to express their solidarity with the families... by coming together in mosques or taking part in peaceful demonstrations," Al Jazeera quoted him as saying.

The opposition rallies are expected to be held in front of the United Nations offices and at Imam Square, the network said.

Supporters of the defeated reformist candidate held a fifth day of rallies in the Iranian capital on Wednesday afternoon, in defiance of a government ban.

The country's supreme leader, Ayatollah Ali Khamenei, has declared his support for Ahmadinejad, calling him the "elected president." However, Khamenei has not been seen in public since the election.

The Guardian Council, which oversees elections, proposed a limited vote recount on Tuesday to appease protestors, but the offer was rejected.