TEHRAN, Iran — Hard-line Iranian protesters stormed British diplomatic compounds Tuesday, hauling down the Union Jack, torching an embassy vehicle and pelting buildings with petrol bombs in what began as an apparent state-approved show of anger over the latest Western sanctions to punish Tehran for defiance over its nuclear program.

The hours-long assault on the British Embassy and a residential complex for staff — in chaotic scenes reminiscent of the seizing of the U.S. Embassy in 1979 — could push already frayed diplomatic ties toward the breaking point.

Iran’s parliament approved a bill Sunday to downgrade relations with Britain, one of America’s closest allies with diplomatic envoys in the Islamic Republic.

Calling Tuesday’s attack “outrageous and indefensible,” British Prime Minister David Cameron said that Iran’s failure to defend the embassy and its staff was a disgrace and would have “serious consequences.”

The late-afternoon demonstration outside the British Embassy was organized by pro-government groups at universities and Islamic seminaries, and could not have taken place without official sanction. However, such anti-Western rallies often draw ultraconservative factions such as the basiji, a paramilitary group run by the powerful Revolutionary Guard that is directly controlled by Iran’s ruling theocracy.

“Death to England!” some cried outside the compound in the first significant assault of a foreign diplomatic area in Iran in years.

Chants called for the closure of the embassy and called it a “spy den” — the same phrase used after militants stormed the U.S. Embassy in Tehran after the 1979 Islamic Revolution and held 52 hostages for 444 days. In the early moments of that siege, protesters tossed out papers from the compound and pulled down the U.S. flag. Washington and Tehran have had no diplomatic relations since then.

Britain’s Foreign Secretary William Hague downplayed suggestions of a hostage situation, saying there had been “confusing” reports coming out of Iran.

By nightfall — more than three hours after the assaults began — Iranian authorities appeared to have regained control of both British compounds. Riot police surrounded the embassy compound and officials said all protesters were driven out.

But sporadic clashes persisted, including some where police fired tear gas to disperse crowds, according to Fars, a semo-official Iranian news agency. Some protesters were arrested, it said.

The rally outside the British Embassy — on a main street in downtown Tehran about a mile from the former U.S. Embassy — included protesters carrying photographs of nuclear scientist Majid Shahriari, who was killed last year in an attack that Iran blamed on Israeli and British spy services.

The U.S. and many allies fear that Iran’s nuclear program could eventually lead to nuclear weapons. Tehran says it only seeks reactors for energy and research, but will not give up the technology to make its own nuclear fuel.

Meanwhile on Monday, the U.S., Britain and Canada announced more sanctions intended to further isolate Iran’s economy.

A senior U.S. official has dismissed Iran’s threats against NATO missile defense installations in Turkey ahead of a visit by U.S. Vice President Joe Biden to the key U.S. ally and linchpin of NATO’s southern flank.

Under the NATO plans, a limited system of U.S. anti-missile interceptors and radars already planned for Europe — to include interceptors in Romania and Poland as well as the radar in Turkey — would be linked to expanded European-owned missile defenses. That would create a broad system that protects every NATO country against medium-range missile attack.

Printed on Wednesday, November 30, 2011 as: Iranian students sack British embassy