The European Union condemned storming of the British embassy in Tehran with EU foreign affairs chief Catherine Ashton calling on the Iranian government to fulfil its international obligations in line with the Vienna Convention to protect diplomats and embassies, dpa reported.
While condemning the storming as violation of international laws, German Foreign Minister Guido Westerwelle ordered the summoning of the Iranian ambassador to Berlin.
French Foreign Minister Alain Juppe also condemned Tuesday's incident
"Once more the Iranian regime has provided proof of the little consideration it has for international law," Juppe said in a statement.
"In these unacceptable circumstances, France shows complete solidarity with Britain," said Juppe, for whom the attack was a "flagrant and scandalous violation of the Vienna Convention."
The United States also weighed in, urging Iran to live up to its international obligations.
A group of Iranian students on Tuesday stormed the British embassy in Tehran, tearing up documents and pictures of Queen Elizabeth II, in the latest instalment of a brewing diplomatic row between the two countries.
Hundreds of students held a protest outside the British embassy, demanding the expulsion of the country's ambassador to Iran.
The demonstration, initially peaceful, changed in tone when some of the students defied anti-riot police stationed at the embassy gate and climbed over the building's wall.
An estimated 10 to 20 students succeeded in getting into the compound, where they started a fire and removed the Union Jack, a policeman at the site said. Several embassy vehicles were also set alight.
Reports that up to six people had been taken hostage and later freed could not be confirmed.
Such reports had raised the spectre of the 1979 hostage crisis, when more than 60 US nationals were taken hostage after Islamist students took over the United States embassy. Some were held for more than a year.
Those who stayed outside the embassy on Tuesday threw stones at its windows and shouted "Death to England" and "Get away England."
Britain's Foreign Office expressed outrage at the incident and confirmed that the demonstrators had vandalized the property.
"We are outraged by this. It is utterly unacceptable and we condemn it," it noted in a statement.
"Under international law, including the Vienna Convention, the Iranian government have a clear duty to protect diplomats and embassies in their country and we expect them to act urgently to bring the situation under control and ensure the safety of our staff and security of our property," a statement out of London said.
Britain also summoned the Iranian charge d'affaires over the storming, Foreign Secretary William Hague said in a statement.
"We hold the Iranian government responsible for its failure to take adequate measures to protect our embassy," Hague said.
Hague said his Iranian counterpart had apologized, but added: "This remains a very serious failure by the Iranian government."
All British embassy staff and their dependents in Tehran had been accounted for, according to the most recent information, Hague added.
The Iranian Foreign Ministry distanced itself from Tuesday's incident.
"The Foreign Ministry deplores the unacceptable actions of some of the protesters, which happened despite efforts by police and special forces to prevent them," the ministry said in a press statement.
"We have always respected international rules and regulations with regards to the immunity of diplomatic missions and therefore started immediate investigations of the incident through legal channels," the statement added.