Relations between Britain and Iran entered a new low Friday when Tehran's diplomats left their London postings following an assault by demonstrators on the British embassy in Tehran earlier this week.

A Foreign Office spokesman in London confirmed that all diplomatic staff at the Iranian embassy had left Britain.

The diplomats arrived at Tehran's Mehrabad airport early Saturday morning and were greeted by officials and a group of students.

About 150 hard-liners waiting with flower necklaces had gathered at the airport to give the roughly two dozen diplomats and their families a hero's welcome. But the Iranian government, apparently opposed to any high-profile display that could worsen the fallout, took the diplomats off unseen from a backdoor, reflecting Iran's own internal political rifts.

Their departure was in line with the decision announced Wednesday by Foreign Secretary William Hague, who ordered the diplomats to leave Britain within 48 hours.

Britain had earlier that day closed its embassy in Tehran, which was stormed and ransacked by radical protesters on Tuesday.

Hague said the expulsion of the Iranian diplomats did not amount to a total severing of ties, but reduced relations between the two countries to the "lowest level consistent with the maintenance of diplomatic relations."

After years of difficult relations, and in view of the rising international tension over Iran's nuclear program, it remained uncertain Friday if, and when, full diplomatic ties between London and Tehran would be restored.

The attack on the embassy was roundly condemned by the United States, the United Nations and western countries, and prompted a new round of sanctions on Iran by the European Union (EU).

Speaking in London Friday, Britain's ambassador to Iran, Dominick Chilcott, described as "terrifying" the attack during which fires were started and protestors "rampaged" through the building.

He and his staff, who locked themselves into safe areas during the attack, had "no idea" how the situation would end, said Chilcott.

It would be "untrue to say" that the "thought of a hostage situation" had not gone through his mind, said Chilcott, who was only appointed to the post in October.

Meanwhile in Tehran, a group of Iranian students said Friday they would fast for three days to commemorate their country's severing ties to Britain.

"For commemorating and cheering the severance of ties with England, students throughout Iran will make a three-day fasting," the office for Unity Consolidation, the main students' organization in Iran, said in a statement carried by the ISNA news agency.

While fasting is mainly practiced in the Muslim month of Ramadan, some Muslims also fast outside Ramadan to commemorate what they view as a positive development or event.