Protesters gesture on a street in Tehran in this undated photo posted online on Sunday. Iranian opposition leader Mir Hossein Mousavi urged his supporters to continue their protests over the disputed presidential election. (Twitter/Reuters)

Security officials in Iran used tear gas and bullets to disperse a crowd of reformist supporters in Tehran on Monday after the Revolutionary Guard had threatened to crush any protests.

Witness accounts from Tehran said between 200 and 1,000 supporters of reformist leader Mir Hossein Mousavi had gathered in Haft-e Tir Square after the warning was issued by the country's elite military force.

Many of the demonstrators carried black candles and wore green ribbons as a show of solidarity.

After riot police fired tear gas and shot bullets into the air, people were forced to leave the area and were not allowed to congregate even in small groups, according to eyewitness reports.

"There is a massive, massive, massive police presence," a woman who asked not to be identified told The Associated Press. "Their presence was really intimidating."

Meanwhile, Britain, accused by Iran of fomenting post-election unrest, said it was ordering the families of diplomats and other officials based in Iran to leave — the first country to do so as Iran's worst internal conflict since the 1979 Islamic Revolution escalated.

'Revolutionary confrontation'

Earlier Monday, the Revolutionary Guard said in a statement that there will be a "revolutionary confrontation" if demonstrators continue to take to the streets.

Demonstrators must "end the sabotage and rioting activities," said the statement, adding that the protests amount to a "conspiracy" against Iran.

A man uses a mobile phone to record images of a protest in Tehran in this undated photo made available on Monday. (Reuters)

Canadian Prime Minister Stephen Harper took issue Monday with the Iranian response to protests in Tehran.

"The reaction of the Iranian authorities to the demonstrations in Iran is wholly unacceptable," he said in a statement. "The regime has chosen to use brute force and intimidation in responding to peaceful opposition regarding legitimate and serious allegations of electoral fraud.

"Basic human rights, including freedom of assembly and freedom of expression, are being ignored," Harper said.

President Mahmoud Ahmadinejad's landslide re-election on June 12 has spurred allegations of vote-rigging and sent tens of thousands of supporters from both sides into the streets for massive protests.

Abbas Ali Kadkhodaei, spokesman for the 12-member cleric Guardian Council, was quoted on state TV Monday as saying a probe into the disputed election results has found that in 50 constituencies there were more votes cast than there were registered voters.

But that "has no effect on the results of the election," which saw Ahmadinejad winning by a 2-to-1 margin, Kadkhodaei said.

Weekend crackdown

Ayatollah Ali Khamenei, the unelected supreme leader, told Iranians on Friday that Ahmadinejad's win is valid and also warned against continued protests of the results.

At least 10 people were killed in clashes Saturday between demonstrators and police and the feared Basij militia. Police said Monday that 457 people were arrested that day alone, without saying how many have been arrested throughout the week of turmoil.

Official figures say 17 people have died in the week of unrest. But searing images posted online hint the true casualty toll may be higher.

At a press conference in Washington, Iran's former crown prince, Reza Pahlavi, condemned Khamenei's suggestion that disputing the election results was an attack against Islam.

In an emotional statement, Pahlavi urged the "sovereignty of the ballot box" be protected.

"Already invested is the blood of my brave countrymen, with energy and support in every corner of Iran — the globe will not rest until it achieves unfettered democracy and human rights in Iran," Pahlavi said.

Mousavi has alleged massive and systematic fraud in the election.

The Guardian Council was ordered to conduct an investigation into the election results.

According to government officials, Ahmadinejad won 62.6 per cent of the vote, while Mousavi garnered 33.75 per cent in a contest that appeared to divide urban and rural voters.

The Guardian Council had said it would conduct a partial recount at disputed polling stations, and will examine 646 complaints regarding the election results, including allegations of shortages of ballots, people on site trying to force citizens to vote for a particular candidate and expelling candidates' representatives from polling stations.

'The country belongs to you'

Mousavi had indicated he did not expect the review to be successful. He alleges the Guardian Council is not neutral and supports Ahmadinejad. He wants an independent investigation.

Mousavi's website said Monday that he continues to support the protests that have been conducted by his backers.

"The country belongs to you.… Protesting lies and fraud is your right," Mousavi said in a statement posted online.

But on Monday most of the opposition movement appeared to be scrambling for a strategy to continue the momentum of the protests that have riveted world attention without putting supporters in peril.

"In your protests, continue to show restraint," Mousavi urged.

Mousavi's website called for supporters to turn on their car lights in the late afternoon as a sign of protest.

In statements posted on the site on Sunday, Mousavi said he would "never allow anybody's life to be endangered because of my actions" and again called for fraud claims to be investigated by an independent board.

Protesters frightened but determined

A journalist who works for a Western news organization, who asked that his identity not be released for fear of reprisals, told CBC News he believes around 10,000 protesters were out on the streets of central Tehran on Monday.

"It's quite amazing what we saw this afternoon, because people were not expecting demonstrators to come out again after the brutal attack of riot police and the government against innocent people on Saturday night," he said in a phone interview from Tehran. An injured man is helped in Tehran on Sunday. (Reuters)

The journalist said he thinks the government has brought Revolutionary Guards from other provinces to clear the streets.

"People are frightened, but it's still amazing that they are continuing. They're still showing victory signs to each other. People are not going to step back very easily."

Iran has ordered journalists for foreign news agencies to stay in their offices, barring them from any reporting on the streets.

Canadian PM calls for release of journalists

"Journalists have been prevented from covering protests and subjected to arbitrary detention and arrest. Foreign press credentials have been revoked," Prime Minister Harper said.

"Canada calls on the Iranian authorities to immediately cease the use of violence against their own people, to release all political prisoners and journalists — including Canadians — who have been unjustly detained, to allow Iranian and foreign media to report freely on these historic events, and to conduct a full and transparent investigation into allegations of fraud in the presidential election.

"The voices of all Iranians must be heard. I have directed the Minister of Foreign Affairs [Lawrence Cannon] to ensure that Canada's views are conveyed to Iran's top representative in Canada," Harper said.

Canadian journalist Maziar Bahari, who works for Newsweek magazine, was arrested in Tehran on Sunday by security officials who entered the apartment he shares with his mother.

Meanwhile, Britain's Foreign Office said Monday that it is evacuating the families of British staff based in Iran amid continued violence. The staff members are not yet being evacuated and other British nationals are not yet being advised to leave the country, the ministry said. With files from The Associated Press