The most pressing problem is securing the release, without charge, of local employees of the British embassy.

Tehran maintains that they helped stoke up anti-regime violence following the re-election last month of President Mahmoud Ahmadinejad.

Seven of the nine embassy staffers seized have since been released, but on Friday a powerful Iranian cleric said some of the nine will be tried for stoking the violence which has seen opposition supporters take to the streets.

For several days European Union nations, pushed hard by Britain, have been seeking to agree concerted action against the Iranian regime, without giving the hardliners an excuse to crack down further on the dissent.

Europe is also keen to avoid alienating the regime at a time when the international community is seeking to persuade Iran to stop enriching uranium for its nuclear programme.

While the West fears this programme has a military aim, Tehran insists that it is purely a civil energy initiative.

"We are discussing a graduated response," one European diplomat said.

Among the measures being considered are preventing some regime figures from securing visas for Europe.

"They could find that obtaining a visa could be more difficult while the British embassy staff remain in detention," the diplomat said.

Another European diplomat confirmed that there could be some kind of visa application freeze which would fall short of the kind of long-term travel ban in place against Zimbabwe President Robert Mugabe and his coterie.

The 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.

A British government spokesman stressed that the first goal of any measures "is to secure the release without charge of our local staff."

The idea of putting the brakes on visa application was discussed by senior European officials in Stockholm on Thursday and negotiations were continuing in Brussels on Friday at a meeting of the EU's political and security committee.

Before the British embassy detentions, the Europeans were already in the front line of international outrage against the crackdown on political protests which followed the June 12 presidential election.

However the response until now has remained merely verbal.

EU foreign policy chief Javier Solana expressed hope Sunday that talks between Tehran and the Group of Six -- Britain, China, France, Germany, Russia and the United States -- over Iran's uranium enrichment activities would resume soon.

Iran, which is labouring under three sets of UN sanctions, has refused to sit down at the negotiating table if it has to suspend uranium enrichment even before the talks begin.

The European fears over reaching the diplomatic tipping point were heightened on Wednesday when a high-ranking Iranian military officer said that Europe had "disqualified" itself from taking part in such nuclear talks because of its interference in the country's internal affairs.

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