David Miliband, Britain’s foreign secretary, said he was “deeply concerned’” by the arrest of British embassy employees working in Tehran, and warned of “strong action” if the detentions did not stop.

His comments follow the detention earlier on Sunday of eight local employees of the British embassy in Tehran, for their alleged involvement in the country’s post-election protests in a further sign of the deteriorating relationship between the UK and Iran.

Speaking at a summit of foreign ministers in Corfu, Mr Miliband said some of the Iranians detained had since been released but added: “We are still concerned about a number of them who to our knowledge have not been released … The numbers are changing hour by hour.”

He added: ”These are hard-working diplomatic staff and the idea that the British Embassy is somehow behind the demonstrations and protests that have been taking place in Tehran in recent weeks is wholly without foundation.”

Britain has strongly protested to the Iranian authorities about the detentions and Mr Miliband is set to discuss the issue with European Union counterparts in Corfu later on Sunday. Western diplomats suggested an EU level statement condemning the detentions was being considered.

Iran has accused western powers of interfering in its internal affairs after the vote, which sparked days of huge demonstrations in which at least 20 people were killed.

The UK has been the main focus of Iranian criticism. In part, this reflects the fact that the US does not have an embassy in Iran. But the troubled relationship between the UK and Iran has a long history, going back to UK involvement in a 1953 coup in the country.

Gordon Brown, the UK prime minister, last week announced that Britain was expelling two Iranian diplomats after the Islamic Republic forced two British diplomats to leave.

Ayatollah Ali Khamenei, Iran’s supreme leader, earlier on Sunday denounced what he called ”interfering statements” by Western officials following Iran’s disputed presidential election. ”If the (Iranian) nation and officials are unanimous and united, then the temptations of international ill-wishers and interfering and cruel politicians would no longer have an impact,” state radio quoted Khamenei as saying. – FT