
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.