Four men dressed in black climbed onto a first-floor balcony at the Iranian Embassy in London and tore down the Iranian flag.
The incident, which occurred on Friday night, was allegedly perpetrated by a group opposing the Iranian regime.
In a video publicized on social media, one of the men can be seen standing on the Embassy porch and holding a blue-and-white flag with Arabic-language writing on it.
Iranian Foreign Ministry spokesman Bahram Ghasemi harshly condemned the incident, and demanded British authorities take immediate action to arrest the perpetrators.
Ghasemi also noted that the British Ambassador to Iran Nicholas Hopton expressed his apologies for the incident, and said police forces are present at the scene and have the situation under control.