The British government has warned that Iran will face “serious consequences” over its failure to protect the UK diplomatic mission in Tehran from attack by hundreds of students and others.

UK Foreign Secretary William Hague charged that the Iranians broke the rules of the Vienna Convention and put the embassy staff’s safety at risk and caused extensive damage.”

Clearly there will be other, further, and serious consequences. I will make a statement updating parliament on this [on Wednesday], Hague said in a statement.

“It amounts to a grave breach of the Vienna Convention which requires the protection of diplomats and diplomatic premises under all circumstances. We hold the Iranian government responsible for its failure to take adequate measures to protect our embassy as it is required to do. I spoke to the Iranian Foreign Minister this afternoon to protest in the strongest terms about these events and to demand immediate steps to ensure the safety of our staff in both embassy compounds. While he said he was sorry for what had happened and that action would be taken in response, this remains a very serious failure by the Iranian government.”

Hague did however note that Tehran police protected some member of the UK staff from an irate crowd outside the compound. According to some reports, some staff members were even taken hostage at one point.

There has been a confusing situation at times as to the whereabouts of certain staff,” Hague added.

“I wouldn't use the term hostage. Clearly there have been situations where the Iranian police have intervened to try to ensure the safety of our staff. We are grateful for that but this situation should never have been allowed to arise in the first place.

Earlier on Tuesday, hundreds of Iranians (including many women) stormed the two compounds housing the British embassy mission and ransacked the buildings, destroying documents, papers and other property to protest against the UK’s support of more sanctions against Iran over the country’s nuclear weapons program.

Two days prior, Tehran expelled the British ambassador to Iran, Dominick Chilcott. The two countries have already significantly downgraded diplomatic and financial ties.

The U.S. government, whose own diplomatic staff in Iran was seized and held hostage for well over a year in 1979, issued a condemnation of the embassy attack.

“The United States condemns in the strongest terms the storming of the British Embassy in Tehran,” the White said in a statement.

“Iran has a responsibility to protect the diplomatic missions present in its country and the personnel stationed at them. We urge Iran to fully respect its international obligations, to condemn the incident, to prosecute the offenders, and to ensure that no further such incidents take place either at the British Embassy or any other mission in Iran. Our State Department is in close contact with the British government and we stand ready to support our allies at this difficult time.”

Officials from the European Union, France and even Russia condemned the attack.

The Iranian foreign ministry apologized for the actions of the protesters.

According to Reuters, the ministry issued the following statement: “The foreign ministry regrets the protests that led to some unacceptable behaviors ... We respect and we are committed to international regulations on the immunity and safety of diplomats and diplomatic places.”