Britain is withdrawing its diplomats from Iran following the attack on its embassy in the capital, Tehran, on Tuesday, diplomatic sources say.The Foreign Office said "some staff" are leaving "for their own safety", but has not confirmed if all its diplomats are being pulled out.
Norway said it has closed its embassy in Tehran, citing security concerns.
Tuesday's attack followed Britain's decision to impose further sanctions on Iran over its nuclear programme.
It led to Iran reducing diplomatic relations with the UK.
'Hasty' Hundreds of protesters - whom Iran described as "students" - massed outside the embassy compound on Tuesday afternoon before scaling the walls and the gates, burning British flags and a car.
Another UK diplomatic compound in northern Tehran, known locally as Qolhak Garden, was also overrun and damaged.Iran said it regretted the incident, which it described as "unacceptable behaviour by a small number of protesters".
According to AFP news agency, a first group of embassy staff are flying out to Dubai.
In a statement on Wednesday, the British Foreign Office said Mr Cameron and Foreign Secretary William Hague had "made clear that ensuring the safety of our staff and their families is our immediate priority".
"In the light of yesterday's events and to ensure their ongoing safety, some staff are leaving Tehran," it said.
British Prime Minister David Cameron has warned of "serious consequences", while the US, EU and UN Security Council also condemned the attack.
Iranian parliament speaker Ali Larijani has described the UN Security Council's condemnation as "hasty", according to state television.
"The hasty move in the Security Council in condemning the students' actions was done to cover up previous crimes of America and Britain while the police did all they could to keep the peace," Mr Larijani was quoted as saying.
On Sunday, Iran's parliament voted by a large majority to downgrade diplomatic relations with the UK in response to Britain's decision to cut financial ties as part of new sanctions.
Norway decided to shut its Tehran embassy "after security concerns" and "in context with the attack on the British embassy", foreign ministry spokeswoman Hilde Steinfeld said.
But but it is not evacuating its staff from Iran, she said.