Armed Men Storm Iranian Embassy in London, Take Down Flag (PHOTO, VIDEO)

Iranian media reported that the slogans chanted by the attackers indicate that they are members of Sadeq Shirazi, a Britain-based Shiite religious sect. BBC Persian contributor Hossein Aghaie confirmed the information on Twitter, adding that Shirazi's son Hossein was recently arrested for criticizing Iran's leadership.

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According to the Fars News Agency, the raiders broke into embassy premises at 4:30 p.m. local time, menaced people on the scene with their weapons, then climbed the embassy building to take down the Iranian flag.

Footage posted on social media shows the men on the embassy's balcony, waving a blue and white flag with inscriptions in Arabic.

​Iran Embassy London UPDATE: Iran's flag taken down, protesters hoist their flag at balcony of Iran Embassy pic.twitter.com/FccV11tlv3

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Iranian Ambassador to the UK Hamid Baeedinejad confirmed reports of the attack, tweeting that "a few followers of [late Shia Muslim cleric Grand Ayatollah Muhammad al-] Shirazi have attacked the Islamic Republic of Iran's Embassy in London and broke the flag mast," adding that the raiders were "chanting slogans against Iranian officials."

In a later tweet, Baeedinejad asserted that all embassy employees are safe and no one was hurt in the incident. He also said that four men had been arrested.

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Iranian Foreign Ministry spokesperson Bahram Qassemi told FNA that an investigation into the case has been launched.

"The British government is duty-bound to seriously and decisively fulfill its responsibility to protect the Islamic Republic of Iran's diplomats and diplomatic centers and immediately arrest and prosecute those who have trespassed the diplomatic sanctuary," the spokesperson said.

The Iranian Foreign Ministry reportedly sent a letter to the British embassy in Tehran complaining about the slow security response by London police, citing reports that they took no action for several hours after the attack.