Iran has drawn more international criticism for failing to stop a mob assault on the British embassy in Tehran, with U.N. Secretary General Ban Ki-moon and U.S. Secretary of State Hillary Clinton adding their voices to the condemnations.

Mr. Ban's office said Wednesday he expressed shock and outrage about the previous day's incident as he met with a British official on the sidelines of an aid conference in Busan, South Korea. The U.N. chief welcomed called on Iran to investigate the British embassy attack and take measures to avoid any repetition there or at other diplomatic missions.

The U.N. Security Council also issued a statement condemning the incident, in which Iranian Islamist activists barged into the main British embassy compound as police looked on. The protesters chanted “Death to Britain,” smashed windows, threw documents out of the building and set fire to a car. Another group of Iranians also stormed a British diplomatic complex in northern Tehran.

Secretary Clinton strongly condemned the assaults as an “affront not only to the British people but also to the international community.” Clinton also was speaking on the sidelines of the Busan aid conference. 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 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.

British Prime Minister David Cameron said Tuesday Iran faces “serious consequences” for failing to defend the British compounds. British authorities said all of their diplomatic personnel in Tehran were accounted for.

U.S. President Barack Obama called on Iran to hold those responsible for the assaults to account.

Iran's parliament responded to the British sanctions on Sunday by approving a measure to reduce diplomatic and economic ties with Britain. It requires the British ambassador to leave Iran within two weeks, leaving a charge d'affaires to run the embassy. Tehran's economic relations with London also will be reduced to a minimum.