However, the anti-riot police were seen at the early hours of the demonstration, calm but alert, standing on both sides of the street, observing the surge of the people who refrained from chanting provocative slogans.

On Sunday, Mousavi made an appeal to his supporters on his website to stage a rally on Monday to hear his words "since there is no means available for informing the people."

"The reason for such a participation is the blockage of all the canals for informing people to avoid any violation," the announcement said.

Mousavi's website, Ghalam News, was unblocked on Monday after a two-day ban and after his meeting with the Supreme Leader Ayatollah Seyyed Ali Khamenei on Sunday evening.

A supporter of Iran's former Prime Minister Mousavi holds a slogan during a rally in Tehran, capital of Iran, June 15, 2009. [Xinhua]

During the meeting, Iran's Supreme Leader ensured Mousavi that he has ordered the Guardian Council to investigate the claims of fraud in the recent presidential election.

"The Guardian Council has been emphasized to carry out investigation carefully," Khamenei was quoted as saying by the State TV.

He also told the former prime minister to pursue his appeal against the election result in a legal way.

"You are different from those people (rioter protestors on the streets) and you are advised to keep manners and calmness," Khamenei said.

Iran's Supreme Leader has urged supporters of both the winner and the defeated candidates to avoid provocative behavior.

Mousavi has already appealed for Iran's Guardians Council to cancel the country's June 12 presidential election result, a statement posted on his website said on Sunday.

"Today, I wrote a letter to the Guardian Council asking them to cancel the result of the recent (presidential) election," Mousavi said in the statement.

On Saturday afternoon, Iran's Interior Minister Sadeq Mahsouli said that the incumbent President Mahmoud Ahmadinejad won 62.63 percent of the total ballots during Friday's vote, while Mousavi got 33.75 percent.

After the official declaration, Mousavi protested "strongly" in a statement the "obvious" violations in Iran's presidential election.

(Xinhua News Agency June 16, 2009)