Britain says it is withdrawing some of its embassy staff from Iran following Tuesday's mob assaults on British diplomatic compounds in the capital, Tehran.

In a statement Wednesday, the British foreign office says the safety of British embassy personnel and their families is London's immediate priority. It did not say how many staff are leaving Iran or when.

Western diplomats told the French news agency that the first group of British evacuees were at Tehran's airport Wednesday, waiting to be flown to Dubai.

British Prime Minister David Cameron said Tuesday Iran faces “serious consequences” for failing to defend the British compounds from Islamists who barged into them as police looked on. The protesters chanted “Death to Britain” as they smashed windows of the main embassy building, threw documents outside and set fire to a car. Another group of Iranians stormed a British diplomatic complex in northern Tehran. The assaults followed followed Britain's decision to impose new economic sanctions against Iran over its alleged nuclear weapons program

The attacks drew more international criticism Wednesday. U.N. Secretary-General Ban Ki-moon's office said he expressed shock and outrage as he met with a British official on the sidelines of an aid conference in Busan, South Korea. The U.N. chief called on Iran to investigate the British embassy break-in and take measures to avoid any repetition there or at other diplomatic missions.

Secretary of State Hillary Clinton, also in Busan, strongly condemned the assaults as an “affront not only to the British people but also to the international community.” She said Washington expects Iran to protect the lives and properties of diplomats in accordance with international conventions.

The Iranian protesters were angry about Britain's decision to cut business dealings with all Iranian banks as part of coordinated sanctions with the United States and Canada announced last week. The Western powers said the sanctions were a response to Iran's pursuit of a nuclear program that U.N. experts say appears designed to build nuclear weapons. Iran says its nuclear program is peaceful.

Iran's parliament responded to the British sanctions on Sunday by approving a measure to reduce diplomatic and economic ties with Britain.

The U.N. Security Council issued a statement condemning the embassy assaults on Tuesday.