TEHRAN, Iran — Hard-line Iranian students stormed British diplomatic sites in Tehran on Tuesday, bringing down the Union Jack flag, burning an embassy vehicle and throwing documents from windows in scenes reminiscent of the seizing of the U.S. compound in 1979.

The mob surged past riot police into the British Embassy complex — which they pelted with petrol bombs and stones — two days after Iran’s parliament approved a bill that reduces diplomatic relations with Britain following London’s support of recently upgraded Western sanctions on Tehran over its disputed nuclear program. Flames shot out of a sport utility vehicle parked outside the brick building.

Demonstrators outside the embassy also burned British flags and clashed with police as the rally, which had been organized by student groups at universities and seminaries.

Less than two hours later, police appeared to regain control of the site. But the official IRNA news agency said about 300 protesters entered the British ambassador’s residence in another part of the city and replaced British flags with Iranian ones. The British Foreign Office harshly denounced the melee and said Iran has a “clear duty” under international law to protect diplomats and offices.

“We are outraged by this,” said the statement. “It is utterly unacceptable and we condemn it.”