(AP) - EDITOR'S NOTE: Iranian authorities have barred journalists for international news organizations from reporting on the streets and ordered them to stay in their offices. This report is based on the accounts of witnesses reached in Iran and official statements carried on Iranian media.

A powerful cleric said Friday that Iran will put British Embassy staffers on trial for fomenting postelection turmoil, a step that would likely increase Iran's isolation and alienate Western nations that have been trying to keep options open with Tehran despite its crackdown on protesters.

The announcement fueled calls in Europe for tougher action against Tehran. Britain is pressing for members of the European Union to pull their ambassadors out of Tehran to protest the staffers' arrests last week.

The standoff is a test of how far Iran's clerical rulers are willing to go to shore up their position at home after the wave of protests _ even if they risk wrecking possibilities for dialogue between Tehran and the West, a major policy goal of President Barack Obama that Tehran cautiously welcomed.

After quashing the street demonstrations, Iran's leadership has been trying to erase any lingering doubts about the legitimacy of President Mahmoud Ahmadinejad by portraying the unrest as sparked by foreign meddling, not by public anger over the June 12 election, which the protesters said was fraudulent. Prosecuting the detained Iranian members of the British Embassy staff could help boost its case before the Iranian public.

At the same time, the arrests test the U.S. and Europe's policy, which has so far been to avoid an overly harsh reaction to Iran's postelection crisis. The West has been wary of condemnations of Iran's leadership, in part for fear of undermining prospects for future talks with Tehran, particularly over its controversial nuclear program.

So far, the EU has taken an incremental approach. On Friday, a day after issuing a public call for the staffers' release, governments across the 27-nation bloc summoned Iran's ambassadors to present the demand in person.

Swedish Foreign Minister Carl Bildt said the EU's "escalatory approach to Iran was working."

But French President Nicolas Sarkozy said his country backs Britain's push for tougher action, "so that Iranian leaders will really understand that the path that they have chosen will be a dead end."

British Foreign Secretary David Miliband said his country is "deeply concerned" about the personnel, who he said "have not engaged in any improper or illegal behavior." He said he would speak with Iranian Foreign Minister Manouchehr Mottaki about the issue.

Word of the trials came from Ayatollah Ahmad Jannati, an ultra-conservative who is one of the most prominent figures in Iran's clerical leadership and is close to the country's supreme leader.

Jannati took a tough line in a sermon to thousands of worshippers attending Friday prayers at Tehran University, accusing Britain of being behind the protests.

London "designed a velvet revolution" to topple Iran's Islamic government and the detained staffers confessed to their role, he told the crowd, where some chanted slogans against the U.S. and Israel.

"In these events, their embassy had a presence," he said. "Some people were arrested. Well, inevitably, they will be put on trial."

He did not say how many staffers will be tried or on what charges. Earlier Iranian officials said all but one of the nine embassy personnel originally arrested had been released, but British officials say two are being held.

Government officials could not be reached on Friday for confirmation the staffers would be tried. Jannati does not hold a position in the government, but is the head of the Guardian Council, a powerful body in the clerical hierarchy that stands above the elected government.

The council oversees elections, and it carried out a partial recount which was ordered after Ahmadinejad's pro-reform rival Mir Hossein Mousavi cried fraud and said he was the victor. The recount ultimately upheld Ahmadinejad's election victory.

Supreme leader Ayatollah Ali Khamenei declared the results would stand, and ruling clerics promptly called the elections "pure" and "healthy."

Giant protests erupted in Tehran and other cities over the results, but they were put down in a tough crackdown after Khamenei declared unrest would no longer be tolerated. Police say 20 "rioters" were killed during the violence. During his sermon, Jannati said seven or eight members of the paramilitary Basij militia were also killed. Basijis took a leading role in putting down the protests, often clashing with demonstrators.

There have been no street protests since Sunday, but Mousavi appears driven to maintain his opposition and even to raise the stakes. In a defiant statement on Wednesday, he said he considered the government illegitimate and demanded political prisoners be released. Still, he has been laying low, making no public appearances for days amid calls by many hard-liners for him to be prosecuted.

In major cities across Iran, clerics delivering Friday prayer sermons told worshippers to accept the supreme leader's ruling on the results, according to transcripts on the state news agency IRNA.

In the northern city of Rasht, Ayatollah Zeinolabedeen Ghorbani said "anyone still saying they don't accept the results ... should be ashamed of themselves as a believer and a Muslim."

Jannati's message in his sermon was clear _ that supreme leader Khamenei had guided the country out of the crisis. "A nation that has rule by the cleric (the supreme leader) and the law does not leave a problem unsolved," he told the crowd.

He indirectly accused Mousavi of treason, pointing out that Ayatollah Ruhollah Khomeini, leader of Iran's 1979 Islamic revolution, once said that "anyone disrupts unity has not only committed a sin but also has committed treason against the Islamic Republic and the system."

Jannati demanded that those involved in the protests "repent and ask God to forgive them."

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Keath reported from Cairo. Associated Press correspondent Ali Akbar Dareini in Tehran, Iran, contributed to this report.