BRUSSELS:EU nations on Friday summoned Iranian ambassadors in protest over the detention of British embassy employees in Tehran, a source close to the Swedish EU presidency said.

"We are summoning the Iranian ambassadors throughout the European Union and we will be monitoring the situation next week concerning the local personnel from the British embassy," the source told AFP.

"All options remain open," he added.

The summoning of ambassadors and charge d'affaires "is happening during the day, some have already summoned the envoy there," another diplomat said.

A total of nine local staff at the British embassy in Tehran were initially arrested late last month but the British government said seven have been released, while Iranian state television has said only one remains in custody.

A powerful Iranian cleric said on Friday that some of the embassy staff arrested for allegedly stoking post-election unrest will be put on trial in a move set to plunge already strained ties to a new low.

Iran accuses the British embassy employees of instigating riots in unrest that erupted over the disputed re-election of President Mahmoud Ahmadinejad, which his rivals say was fraudulent and marred by widespread irregularities.

"We maintain the need for a strong and collective response from the EU to ensure the release of the remaining staff in detention and we are working well with our European partners on a step-by step approach," a British government official said.

The 27 EU nations are monitoring the situation carefully, particularly the unconfirmed comments that some of the detainees would be tried, diplomats said.

"All options remain on the table. We will see how events progress over the weekend and then return to the matter next week," one said.

The idea of summoning Iranian ambassadors arose from a meeting of EU political directors in Stockholm on Thursday.

It was endorsed at a meeting of the EU's Political and Security Committee in Brussels on Friday.

One European diplomat said that pulling out European ambassadors from Tehran remained an option, but stressed the measured approach.

"Since the idea of pulling out all EU ambassadors has been floated (on Sunday) seven out of the nine embassy detainees have been freed. This is a measured approach and we have to give some flexibility to those in Iran seeking to help us to obtain our goals," she told AFP.

"You have to link your response to what is going on," she added.

The idea of pulling out ambassadors had also received an unenthusiastic response among London's EU partners who feel it is the kind of radical measure which could complicate the resumption of the nuclear talks.