The European Union (EU) on Tuesday condemned the storming of British diplomatic compounds in Tehran.

"It is with extreme concern that I have learnt that the premises of the Embassy of the United Kingdom in Tehran have been overrun by demonstrators. I strongly condemn this totally unacceptable incursion," said Catherine Ashton, the EU foreign policy chief in her statement.

"I call on the government of the Islamic Republic of Iran immediately to fulfill its international obligations, including the Vienna Convention, to protect diplomats and embassies, " she said.

"I am following developments closely and remain in contact with the UK authorities and EU Member States," Ashton added.

Hundreds of angry Iranians staged a protest outside Britain's main embassy in downtown Tehran early Tuesday, and some of them broke into the compound. Similar incident took place in a second British diplomatic compound in north Tehran.

British Foreign Office has said the intrusion was "utterly unacceptable," while Iran's Foreign Ministry expressed "regret" over the incidents.