LONDON — Iranian protesters screaming "death to England" stormed the vast British embassy compound and a diplomatic residence in Tehran on Tuesday, torched at least one vehicle, tore down the Union Jack, ransacked offices and briefly held six staff members captive during an officially approved protest of economic sanctions against Iran's suspect nuclear-energy program.

The assault, reported by Iranian news services and broadcast on Iranian television, ended after several hours and constituted the most serious breach between Britain and Iran in more than 20 years. The images evoked memories of the siege of the U.S. Embassy after the Iranian revolution of 1979.

Britain's Foreign Secretary, William Hague, expressed outrage. He said that Britain held Iran's government responsible and promised "other, further and serious consequences."

Hague said in a statement that both British compounds had been stormed by "several hundred people, putting the safety of our diplomats and their families at risk and causing extensive damage to our property." All British staff were accounted for, he said, without making direct reference to the six who had been briefly held. He warned British nationals against all but essential travel to Iran and advised the small number in the country to stay indoors.

The United States and European Union also rushed to condemn the assault, and the U.N. Security Council issued a statement calling upon Iranian authorities to protect foreign diplomats and embassy property and to "respect fully their international obligations in this regard."

President Obama, speaking about the assault during a meeting with Prime Minister Mark Rutte of the Netherlands at the White House, said he was "deeply concerned" that Iranian authorities had permitted it to happen. "For rioters essentially to be able to overrun the embassy and set it on fire is an indication that the Iranian government is not taking its international obligations seriously."

The protest was organized to mark the anniversary of the death of nuclear scientist Majid Shahriari in an attack Iran blamed on British and Israeli intelligence agencies.

A few hundred demonstrators gathered outside the British Embassy in downtown Tehran, chanting "death to England" and demanding the immediate withdrawal of Ambassador Dominick Chilcott.

Iranian news agencies said about 50 protesters invaded the offices of the enormous walled compound housing the British Embassy and its manicured grounds in a busy neighborhood in the heart of Tehran, where they tossed gasoline bombs and hoisted the Iranian flag in place of the British banner. They ripped down satellite dishes, tossed out papers and carried away a portrait of Queen Elizabeth II.

About 200 to 300 others got into a British diplomatic residence facility a few miles north of the embassy, called Qolhak Garden, which also houses a school.

Iran's semiofficial Fars News Agency said that police officers freed six British staff members who had been surrounded by the Qolhak Garden protesters and that 12 of those protesters were later arrested.

After the mayhem was brought under control by Iranian police and security officers, Iran's Foreign Ministry expressed "regret" over the assault, said the violence had been carried out by a small number of protesters despite preventive efforts, and that wrongdoers would be prosecuted, Agence France-Presse reported from Tehran.

Fars said that the police had to use tear gas to disperse some protesters inside the embassy grounds and that "a number of protesters have been wounded." The agency said the protest ended after Brig. Gen. Ahmad Reza Radan, the deputy police chief, warned any recalcitrant protesters they would face a "tough police confrontation" if they did not leave the embassy.

Earlier, television images from the scene showed protesters, some armed with Molotov cocktails, rampaging through offices strewn with papers, and at least one vehicle inside the compound on fire.

Although the official Iranian media characterized the protest as a genuine outburst of popular anger against Britain that may have gotten out of hand, it was clear that the event had been ordained by the authorities, who in the past have orchestrated attacks on embassies, intervening only at the last minute. Iran's security forces and its Basij militia have maintained strict control over mass protests in Iran since the disputed election of 2009.

Images transmitted from the scene showed riot police standing by during the assault and later helping protesters inside the embassy grounds go back to the street outside. Press TV, a government news website, said police dispersed the demonstrators and were "protecting the embassy building and the documents inside."

It was not clear if the embassy assault was purposefully designed to mirror the storming of the U.S. Embassy on Nov. 4, 1979, that led to the estrangement with Washington that has lasted to this day. But Iran's post-1979 revolutionary leaders have always harbored a special antipathy toward Britain, commonly regarded as the older cousin of the United States.

A day before the embassy assault, Supreme Leader Ayatollah Ali Khamenei singled out Britain in a speech as an icon of Western imperialist arrogance, saying it "has a history of humiliating nations, destroying cultural and civilization heritage and taking control of their resources."

The Associated Press identified the embassy assailants as hard-line Iranian students, who were said to have burst into the building and thrown documents from windows.

They also chanted: "The embassy of Britain should be taken over!"

The demonstrators were angry about British support for stepped-up Western sanctions after the International Atomic Energy Agency released a report saying Iran may be secretly working to develop a nuclear weapon.

Chancellor of the Exchequer George Osborne announced last week that Britain was severing financial ties with Iranian banks, which British officials accuse of facilitating Tehran's nuclear program. Iran says the program is only for civilian purposes.

Information from the Los Angeles Times

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Britain said it is withdrawing some staff and dependents from its Tehran embassy. The Foreign Office refused to say Wednesday how many people were being removed or give other details. "Ensuring the safety of our staff and their families is our immediate priority," it said.

The Associated Press