Reformist leader Mir Hossein Mousavi has been told by Iran's Interior Ministry to apply in person, a week ahead of time, for any future protests. (Vahid Salemi/Associated Press)

Iranian opposition leader Mir Hossein Mousavi agreed Friday to seek government permission to hold any future rallies on Iran's disputed election results as a leading cleric demanded that those behind last week's protests be harshly punished.

"I want the judiciary to … punish leading rioters firmly and without showing any mercy to teach everyone a lesson," senior cleric Ayatollah Ahmed Khatami said during a prayer sermon at Tehran University.

The election's outcome, which handed a 2-to-1 victory to President Mahmoud Ahmadinejad, has spurred allegations of vote-rigging and sent tens of thousands of protesters from both sides into the streets.

"Anyone who takes up arms to fight with the people, they are worthy of execution," Khatami said.

Those who disturbed the peace and destroyed public property in the wake of the June 12 vote are "at war with God" and should be "dealt with without mercy," he said.

Meanwhile in Stockholm, police said about 150 demonstrators stormed the Iranian Embassy outside the Swedish capital, throwing stones and trying to force themselves into the building.

A police spokesman said one embassy worker was injured as a smaller group of protesters tried to climb through broken windows.

Protest crackdown

Iran's supreme leader, Ayatollah Ali Khamenei, and the country's elite military force, the Revolutionary Guard, have warned against continued demonstrations, and the government has set up a special court to deal with detainees from the rallies.

At least 17 people have been killed in the post-election protests as authorities intensified their crackdown.

In Trieste, Italy, foreign ministers of the Group of Eight countries called for an end to the violence in Iran and urged authorities to find a peaceful solution to the conflict.

In a message posted on his website, Mousavi said he has been told by the Interior Ministry to apply in person, a week ahead of time, for any future protests.

Restrictions on Mousavi supporters

He added he will abide by the order and will seek permission for any future rallies even though unfair restrictions were being imposed.

Two post-election marches and a Tehran rally were allowed to be held by Ahmadinejad's supporters and were "well publicized on state television, seeming to encourage participation with their regularly advertised march routes," Mousavi said.

Mousavi has previously urged supporters not to break the law by continuing protests amid a government crackdown, but he has also said he won't drop his challenge to the election results.

He hasn't led a rally in more than a week.

Mousavi said Thursday he is under increasing pressure to withdraw his electoral challenge from Iran's Guardian Council.

On Friday, Mousavi's website, his main tool to communicate with his supporters since the election, appeared blank, after reportedly being hacked.

Khamenei has ordered a large security detail around Mousavi — ostensibly to protect him, but presumably also to restrict his movements. Authorities have also targeted those close to Mousavi, detaining 70 university professors he held meetings with.

Banned from leaving Iran

The head of Mousavi's information committee, Abolfazl Fateh, has also been reportedly banned from leaving Iran for Britain, where he is a doctoral student.

Despite acknowledging voting irregularities — more ballots were cast than voters registered — in several Iranian districts, the 12-member Guardian Council has said there were no major incidents of fraud and there will not be a new vote.

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

The council again affirmed the results on Friday, saying that the June 12 vote was the "healthiest" election since the 1979 Islamic Revolution.

With files from The Associated Press