The European Union's 27 nations yesterday joined forces to condemn Iran's detention of British staff in Tehran, as tensions escalated between the Islamic republic and the west.

After Iran arrested nine local employees working at the UK embassy in Tehran, EU foreign ministers meeting in Corfu said they would respond firmly to any further "harassment or intimidation [by Iran] of foreign or Iran-ian staff working in embassies".

David Miliband, British foreign secretary, said he was "deeply concerned" by the arrests and warned that their continued detention was "unacceptable''.

The intensity of the diplomatic stand-off was underscored by the EU statement in which foreign ministers said they were becoming "seriously concerned" about developments inside Iran, which has in the past fortnight witnessed the greatest upheaval since the 1979 Islamic revolution.

But in a reminder of the delicacy of the diplomacy, the US administration and Javier Solana, the EU's foreign policy chief, said the door was still open for a renewal of talks on Iran's nuclear programme.

Mr Miliband said as of yesterday morning four of the nine staff had been released. The EU statement demanded all should immediately be set free.

Iranian media said the staff had been detained because of their "considerable role" in instigating riots triggered by this month's disputed election result. Hundreds of thousands of people have demonstrated in Tehran and other cities to demand a recount of votes of the June 12 presidential election after the authorities said Mahmoud Ahmadi-Nejad, the hardline incumbent, had secured a sweeping victory.

Iran has repeatedly claimed that UK diplomats have been interfering in the country's domestic affairs. Last week Iran forced two British envoys to leave the country, a decision that triggered an immediate tit-for-tat response by -London.

Mr Miliband roundly rejected Iran's allegations about the local staff yesterday. "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," he said.

The UK has been the focus of Iran's diplomatic protests, partly because the US does not have an embassy in Iran. The troubled relationship between the UK and Iran has a long history, going back to British involvement in a 1953 coup in the country.

Iran's leaders stepped up their attacks on the west yesterday. Ayatollah Ali Khamenei, the supreme leader, denounced what he described as "interfering statements" by western officials. "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 him as saying.

While the street rallies that drew hundreds of thousands have stopped, Mir-Hossein Moussavi, the main challenger to Mr Ahmadi-Nejad, showed no sign of compromise at the weekend. He wrote a letter to the Guardian Council, the constitutional watchdog, insisting that the election results had to be cancelled.

The council has suggested the establishment of a committee - comprised of politicians and candidates' representatives - to supervise a random recount of 10 per cent of the votes.

Mr Moussavi rejected that proposal and insisted the fraud went beyond the counting process. He even accused the council of siding with Mr Ahmadi-Nejad - against its legal obligations to remain impartial.

"I insist again on cancelling the election as the most suitable way forward," he said on his official -website.

Akbar Hashemi Rafsanjani, a former president and rival of Mr Ahmadi-Nejad, broke his post-election silence to call for a thorough examination of the election. He praised Mr Khamenei's decision to give the council time to examine the complaints.

Mr Khamenei, who has ruled out a rerun, again called yesterday for the problem to be resolved by legal channels, in a clear reference to the council. He called on "both sides. not to provoke the feelings of the youth - and do not put people against each other".