Iranian protesters stormed the British Embassy in Tehran today, tossing firebombs and burning documents, but an Iranian news agency has withdrawn a report that six embassy staff members had been taken hostage.

Update at 1:57 p.m. ET: The Iranian Foreign Ministry expressed "regret for certain unacceptable behavior by a small number of protesters in spite of efforts by the police," the BBC reports. "The relevant authorities have been asked to take the necessary measures and look into this issue immediately," the ministry said. The U.N. Security Council condemned the attack "in the strongest terms."

Update at 11:03 a.m. ET: Reuters quotes the Iranian semi-official FARS news agency as saying that police had secured the release of six British Embassy staff who were taken hostage. There were no details. Earlier, the Iranian semi-official Mehr news agency had reported the apparent hostage-taking, but withdrew the report later from its website without explanation.

Update at 10:03 a.m. ET: The Iranian news agency, Mehr, that reported that six staff members at the British Embassy's compound in northern Tehran had been taken hostage, has withdrawn the report from its website with no explanation.

Update at 9:42 a.m. ET: The semi-official FARS news agency reports that thousands of protesters who have gathered in front of the British Embassy are demanding that the British ambassador be expelled and the embassy shut down.

Update at 9:21 a.m. ET: The official IRNA news agency in Tehran says there are about 50 students in the embassy and that police prevented more from entering the compound by stopping them from opening the main gate. IRNA says "security and disciplinary forces" are deployed around the embassy and that police are trying to disperse the crowd with water cannon. IRNA reports that student protesters are chanting "God is the Greatest", "Down with the UK," "Down with the U.S.," and "Down with Israel."

Update at 9:07 a.m. ET: Reuters quotes an unidentified Iranian official as saying the storming of two British Embassy compounds in Tehran was not planned by the government: "It was not an organized measure. The establishment had no role in it. ... It was not planned."

Update at 9 a.m. ET: Reuters quotes the Iranian Mehr News agency as saying six members of the British Embassy staff have been taken hostage by protesters in the northern compound. This has not been confirmed by other sources or British official sources. The Mehr News Agency is owned by the Islamic Ideology Dissemination Organization.

Update at 8:45 a.m. ET: There is no immediate word on casualties or how many embassy employees were inside at the time of the assault, although it occurred after business hours, the Associated Press reports. More protesters poured into the compound as police tried to clear the site.

Update at 8:35 a.m. ET: The Telegraph reports that the British Foreign Office issued a statement condemning the attack on the British Embassy in Tehran:

There has been a incursion by a significant number of demonstrators into our Embassy premises, including vandalism to our property. This is a fluid situation and details are still emerging. We are outraged by this. It is utterly unacceptable and we condemn it. 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.

Update at 8:30 a.m. ET: The official IRNA news agency reports that the embassy has been locked in "a symbolic gesture by a group of Iranian students." It also reports that the students are still there.

Update at 8:25 a.m. ET: Damien McElroy, foreign affairs correspondent for the British newspaper The Telegraph, reports that a group calling itself The Muslim Students Followers of the Supreme Leader claim responsibility for the attack on the embassy and have issued a statement reportedly in blood.

The statement, according to The Telegraph, says:

Our people are not prepared to be humiliated any more under any circumstances and prefer a red death to a condemned life of misery. We are ready to be killed for our aims.

In a throwback to the language used by students who took over the U.S. Embassy in Tehran in 1979, the statement referred to the British Embassy as "another nest of spies that must be shown our wrath and hatred towards it."

Update at 8:18 a.m. ET: The British newspaper The Telegraph reports that gasoline bombs are being thrown inside the compound and that protesters are burning documents seized from offices.

Update at 8:02 a.m. ET: The official Iranian news agency IRNA sent out this urgent report: "The UK Embassy in Tehran has been stormed by a group of Iranian students."

Update at 7:44 a.m. ET: The BBC reports that demonstrators were shown live on Iranian state TV throwing stones at embassy windows and breaking them.

Update at 7:39 a.m. ET: IRNA, the official Iranian news agency reported in advance of the protest that Iranian university students were gathering "to express their wrath at the hostile UK policies towards Iran." It said the meeting was taking place on the anniversary of the assassination of the Iranian nuclear scientist Majid Shahriari.

Here's IRNA's report:

The students have organized the gathering to voice their support for a recent parliament bill which obliges Iranian Foreign Ministry to lower level of ties with the UK. According to the bill, ties with Britain will be reduced to the level of charge d'affaires and thus the UK ambassador has to leave Iran within two weeks.

Update at 7:35 a.m. ET: Dozens of hard-line Iranian students stormed the British Embassy in Tehran today, bringing down the British flag and throwing documents from windows, the AP reports. The students clashed with anti-riot police and chanted "the Embassy of Britain should be taken over" and "death to England."

Original post: The attack came after a crowd of about 1,000 people gathered in front of the building for an anti-British demonstration, CNN reports.

On Sunday, the Iranian Parliament voted to expel the British ambassador and reduce diplomatic relations with the United Kingdom in retaliation for new Western sanctions, according to Iran's IRNA news agency, CNN reports. The vote must go to the Guardian Council for approval.

The British Foreign and Commonwealth Office called parliament's vote "regrettable."

"This unwarranted move will do nothing to help the regime address their growing isolation or international concerns about their nuclear program and human rights record," the office said in a statement, CNN reports. "If the Iranian government acts on this, we will respond robustly in consultation with our international partners."