The European Union decided Friday to summon Iranian ambassadors across the 27-nation bloc in a joint protest against the detentions of staff at the British Embassy in Teheran. The EU called Iran's decision to put detained British Embassy staff on trial "not acceptable." Britain had proposed recalling all EU ambassadors from Teheran as a powerful signal of unity, but the 27-nation bloc settled for a gradual escalation of pressure, Swedish Foreign Minister Carl Bildt said. In a statement, Bildt said the EU's "escalatory approach to Iran was working" and noted that seven of nine embassy employees had been released. The Europeans would review the situation next week unless the remaining staffers are released, said Bildt, whose country holds the rotating EU presidency. French President Nicolas Sarkozy indicated he supported the British request to turn up the heat on the Iranian regime. "France has always wanted to strengthen the sanctions, so that Iranian leaders will really understand that the path that they have chosen will be a dead end," he said in a joint news conference with Swedish Prime Minister Fredrik Reinfeldt. "Now it's up to the British to tell us what they need, what help they need." Sarkozy added that "our solidarity with our English friends is total." The issue poses a difficult challenge for the EU. Recalling diplomats from Teheran would be an extraordinary move and a powerful signal of unity in the wake of Teheran's post-election crackdown. But punishing the regime too harshly also risks spoiling chances of making headway on the critical issue of Iran's disputed nuclear program. "It's not acceptable to file charges against the ones released or to the ones still in custody," Bildt said. On Friday, the head of Iran's powerful Guardians Council said that the British embassy staff, accused of inciting violence in post-election protests, would face trial. Ayatollah Ahmad Jannati, who is close to Iran's supreme leader Ayatollah Ali Khamenei, made the announcement during Friday prayers in Teheran. "Naturally they will be put on trial, they have made confessions," Jannati said. "In these incidents, their embassy had a presence, some people were arrested." Jannati told the thousands of worshippers Friday that the British "had designed a velvet revolution ... In March, they said [in their Foreign Ministry] that street riots were possible during June elections. These are signs ... revealed by themselves." He also said those involved in protests "need to repent and ask God to forgive them." The British foreign office said it was very concerned and urgently seeking an explanation from Iran on the matter. "We are very concerned at these reports and are investigating them," a foreign office spokesperson said. "The allegations that embassy staff were involved in instigating the recent demonstrations are wholly without foundation." Protests were widespread across Iran following last month's presidential election amid claims the vote had been rigged in favor of President Mahmoud Ahmadinejad. At least 20 people were killed in the disturbances and many more arrested by the authorities. On June 27, nine embassy staff were arrested in Teheran accused of playing a role in post-election protests. All except two were eventually released. Teheran has repeatedly accused foreign powers - especially Britain and the US - of meddling and stoking the unrest after the June 12 election. Last month Iran's supreme leader, Ayatollah Ali Khamenei, described Britain as the "most evil" of its enemies.