All Iranian diplomats left Britain on Friday, expelled in response to protesters storming the British embassy in Tehran, hardening a confrontation between Tehran and the West over its nuclear programme.

In Iran, crowds chanted Death to Britain at Tehran University, and a militia linked to the storming of the embassy prepared to greet the returning diplomats as heroes. A hardline cleric denounced the U.N. Security Council and European Union for backing Britain following the embassy storming.

But President Mahmoud Ahmadinejad and Supreme Leader Ayatollah Ali Khamenei remained silent, perhaps reflecting unease within the faction-riven leadership about an incident likely to deepen Iran's international isolation.

Protesters stormed two British diplomatic compounds on Tuesday, smashing windows, torching a car and burning the British flag in protest against new sanctions imposed by London.

The incident followed accusations from Washington of an Iranian plot to assassinate the Saudi ambassador and a report from the U.N. nuclear watchdog suggesting Iran was pursuing nuclear weapons, all contributing to increased diplomatic isolation for Tehran in recent months.

I can confirm that, earlier this afternoon, all diplomatic staff of the Iranian Embassy in London took off from Heathrow airport, a British Foreign Office spokesman said.

After the embassy storming, Foreign Secretary William Hague announced that Britain was closing its embassy in Tehran, ordered the closure of the Iranian embassy in London and gave all Iranian diplomats 48 hours to leave Britain.

Hague said the assault could not have happened without the consent of Iranian authorities.

The Iranian diplomats slipped away quietly. The green, white and red Iranian flag still flew over the Iranian embassy in west London that was the scene of a dramatic six-day siege in 1980 when gunmen seized 21 hostages, two of whom they killed.

Across the street, a dozen protesters opposed to Iran's government chanted Free Iran and urged terrorists to go home. A few police officers stood guard.

Western powers suspect Iran is seeking to develop nuclear weapons but Iran insists its programme is peaceful.

Diplomacy has come to a boil after a report in November by the U.N. watchdog, the International Atomic Energy Agency suggested Iran has worked on a nuclear bomb programme. The United States and Israel have not ruled out military strikes.

REMORSE

Britain's Ambassador to Iran, Dominick Chilcott, said hardliners in the Iranian establishment may have thought confrontation would rally Iranians, but miscalculated how strong the response to the embassy storming would be.

They probably didn't expect us to send home the Iranian embassy in London and, reading between the lines, you can see in the way they have responded to that move, some remorse in having provoked it, Chilcott told the BBC.

The closure of the embassies, by cutting off a channel of communication between Britain and Iran, complicates the search for a diplomatic solution to the nuclear dispute.

Having this tension between Iran and Europe will make those negotiations a lot harder, said Adam Hug, policy director of the Foreign Policy Centre, a London think-tank. It does make the risk of conflict slightly more plausible.

France, Germany and the Netherlands recalled their ambassadors from Tehran for consultations as a protest against the storming of the British compounds.

The EU added 180 Iranian people and entities to its sanctions list on Thursday and laid out plans for a possible embargo on Iranian oil, the lifeblood of the Iranian economy.

The United Nations Security Council said it condemned in the strongest terms the attack, although veto-wielder Russia made clear it saw no need for more sanctions.

ROTTEN ROPE

In Tehran, cleric Ahmad Khatami denounced the EU and Security Council to worshippers who chanted Death to Britain.

If you have just a bit of wisdom, you won't tie your rope to the rotten rope of Britain, he said.

Increasing tensions with the world's fifth biggest oil exporter pushed up global oil prices despite concerns of an economic downturn in the West. Brent crude rose towards $110 a barrel on Friday from a Thursday close of $108.99.

Iran's culture ministry banned foreign media from covering anti-British pro-government protests in Tehran, especially rallies in front of the British Embassy and the Qolhak compound unless authorised in advance, the ministry said in a statement.

Witnesses reported a heavy presence of police at Ferdowsi square, where the British embassy is located.

Life is normal in the area but there are many police officers in the area, said a witness who asked not to be named.

The 135-year-old embassy residence was severely damaged in the onslaught. The ornate building at the centre of the complex has changed little since it hosted a dinner between Soviet leader Joseph Stalin, U.S. President Franklin D. Roosevelt and Britain's Winston Churchill during the 1943 Tehran conference.

One Western diplomat who visited it on Thursday said priceless oil paintings had been slashed and protesters had cut out the face of a portrait of Queen Victoria. There were no reports of harm to staff.

The semi-official Fars news agency reported on Wednesday that 11 hardline protesters detained for storming the British compounds had been released.

Iranian diplomats expelled from London were due to arrive in Tehran in the early hours of Saturday and the hardline Basij militia said it would have a welcoming committee for them at the International Imam Khomeini Airport outside the capital.

Iran's Foreign Ministry expressed regret over the embassy invasion, which it said was a spontaneous overflowing of anger during a peaceful protest by students. Britain says there must have been at least tacit approval by the ruling establishment.

The Iranian reformist website Sahamnews issued a statement by a group of students at the Islamic Azad university condemning the attack and saying the conservative hardliners did not represent the view of most young Iranians.

Misusing the name of student is something we cannot easily let pass. There is no connection between what these people did and the honourable and sensible Iranian students, it said.

Parliamentary speaker Ali Larijani, a long-time rival to Ahmadinejad, condemned the U.N. Security Council reaction to the embassy storming as hasty and devious.

(Additional reporting by Parisa Hafezi; Writing by Parisa Hafezi and Robin Pomeroy; Editing by Peter Graff and Jon Hemming)