London will hit Tehran with new sanctions, officials said, after Iranians protesting prior sanctions stormed the British Embassy as security forces looked on.
The British sanctions, to be imposed as early as Wednesday, will be "robust and resolute," government officials told the Daily Mail.
British Foreign Secretary William Hague -- who with Prime Minister David Cameron expressed outrage at the Tuesday siege -- promised "other, further and serious consequences" and said he would address Parliament Wednesday.
An additional consequence could be other European nations recalling their ambassadors, removing a key channel of communication, The Washington Post reported.
The European Union is to debate new sanctions against Iran Thursday.
Europe remains one of Iran's largest trading partners and a key conduit between the country and Washington, which severed ties after the U.S. Embassy in Tehran was overtaken Nov. 4, 1979.
In the British Embassy siege -- which evoked memories of the U.S. Embassy takeover that led to a 444-day hostage crisis -- young Iranians surged through lines of riot police, ransacked embassy offices, seized classified documents and briefly held six staff members captive, video by the official Iranian English-language TV channel indicated.
The TV channel broadcast the entire assault, which Western diplomats said was led by paramilitary Basij brigades controlled by Iran's Revolutionary Guards and loyal to Iranian Supreme Leader Ayatollah Ali Khamenei.
The Islamist brigades, known for policing morals and suppressing dissident gatherings, consist of young Iranians who volunteer, often in exchange for official benefits.
The force of about 50, chanting "Death to England," ripped the gilded British crest off the embassy, tore down the Union Jack, replacing it with the Iranian flag, tore up portraits of Queen Elizabeth II and threw satellite dishes off the roofs of embassy buildings.
They smashed windows and scattered thousands of papers onto the street, where British, U.S. and Israeli flags were set on fire. Thousands of student protesters rallied in front of the embassy.
About 200 to 300 other rioters got into Britain's 50-acre diplomatic compound, housing British diplomats and their families, in the northern Tehran neighborhood of Gholhak, a few miles north of the embassy. The compound, called Qolhak Garden, is also home to the Tehran War Cemetery and has been at the center of diplomatic tension between Britain and Iran over its ownership and management.
Iran's semi-official Fars News Agency said police officers freed six British staff members who had been surrounded by the Qolhak Garden protesters, adding 12 protesters were arrested.
The attacks, to protest economic sanctions against Iran's suspect nuclear energy program, ended after several hours.
Besides Britain -- which called the attacks "outrageous and indefensible" and said it upbraided Iranian Foreign Minister Ali Akbar Salehi in the "strongest terms" -- the United States, France, EU and U.N. Security Council condemned the assault.
Russia, Iran's closest ally, described it as "unacceptable and deserving condemnation."
Iran's Foreign Ministry expressed "regret" over the "unacceptable behavior by [a] few demonstrators" in spite of preventive efforts, and promised an investigation with wrongdoers prosecuted.