William Hague says diplomats must leave UK within 48 hours, saying storming of British embassy in Iran had backing of regime

The foreign secretary, William Hague, has ordered the expulsion of Iranian diplomats from the UK and announced that the UK is closing its embassy in Tehran, saying that the storming of the mission on Tuesday had the backing of the regime.

Hague said Iranian diplomats would have to leave Britain within 48 hours, and that all British embassy staff in Tehran had now left Iran.

He said that the move would not mean the severance of all ties, as the two countries could continue to have a dialogue at international meetings, as the US has done since the seizure and closure of its embassy in 1979, but the move marks a new low in relations, which have been growing increasingly strained.

The foreign secretary said it was not possible to maintain an embassy in the current circumstances, adding that the estimated 200 protesters who invaded the embassy and the British diplomatic compound yesterday were "student basij militia". The basiji operate as a youth wing of Iran's Revolutionary Guards, one of the most powerful institutions in the country.

Hague said it would be "fanciful" to think that the embassy invasion could have taken place without "without some degree of regime consent".

He added: "If any country makes it impossible for us to operate on their soil they cannot expect to have a functioning embassy here."

Iranian diplomats in London refused to comment on the announcement.

Foreign Office sources said the foreign secretary had made his statement minutes after he received confirmation that the 26 British embassy staff had taken off from Tehran, heading for Britain.

The announcement had been delayed until then for fear "there would be some nutso backlash against our people", the source said.

The fleeing diplomats left the Iranian capital with whatever possessions they could salvage from their homes after the British residential compound in northern Tehran had been completely ransacked, an official said.

"The residential accommodation had been comprehensively trashed. The mob had gone through houses and apartments, wrecking them, nicking things. It was like a gang of feral street kids had been given license to do as much damage as possible," he said.

The crowd had also set fire to the first floor of the embassy, the official said, causing extensive damage. The only staff left at the embassy and the residential compound will be local security staff, who will be asked to prevent the buildings becoming "a playground for local youths".

In the next few days a decision will be made on which country's embassy could act as a UK interests section. In previous low points in UK-Iran relations the Swedes have played that role, but no decision has yet been made.

Hague will now go to Brussels for an EU foreign ministers' meeting looking for support, and for other capitals to call in resident ambassadors to complain.

The message, as one official put it, would be: "If you let your thugs destroy our embassy and assault or scare our staff, you cannot expect to maintain normal civilised relations with the rest of the world."

Earlier on Wednesday, Norway temporarily closed its embassy in Tehran, citing security concerns, and Sweden summoned Iran's ambassador to Stockholm to its foreign ministry. "Iran has a duty to protect diplomatic premises, and authorities there should have intervened immediately," said a Swedish foreign ministry spokesman.

The Scandinavian countries' reactions follow outspoken condemnation of the attack from the US and France. The US secretary of state, Hillary Clinton, said: "The United States condemns this attack in the strongest possible terms. It is an affront not only to the British people but also the international community," she said.

In Iran the attack on the embassy has prompted mixed reactions even among the supporters of the regime. The Iranian foreign ministry last night expressed regret over the "unacceptable behaviour by [a] few demonstrators" and promised an investigation.

But Ali Larijani, the country's powerful parliamentary speaker, told MPs on Wednesday that the attack was the result of "several decades of domination-seeking behaviour of Britain".

Larijani also criticised the UN security council for condemning Tuesday's incident.

"The hasty move in the security council in condemning the students' action was done to cover up previous crimes of Britain and the United States," the semi-official Mehr news agency quoted Larijani as saying during an open session at Iran's parliament.

In contrast , the Iranian foreign ministry said it was committed to protecting diplomatic personnel and said a thorough investigation would be launched.

In Tehran the episode has been seen as the latest episode in an extraordinary power struggle between the conservatives in parliament and the judiciary on one side, and the government of the president, Mahmoud Ahmadinejad, on the other.

Pro-Ahmadinejad supporters have interpreted the recent events as an attempt to hamper the government's efforts to reduce tensions with the international community and undermine the government's foreign policy.

Iranian state agencies, meanwhile, tried to depict Tuesday's events as an spontaneous protest by "university students" and attempted to distance the establishment from the attack.