Seven men have been arrested on suspicion of grievous bodily harm after two people were assaulted outside the Iranian embassy.
The Met Police have said they believe the altercation happened between protesters supporting and opposing the Iranian monarchy, and there were no links to Israel.
Officers had responded to reports of an altercation in Princes Gate in Knightsbridge, west London, shortly after 09:50 BST on Friday, a force spokesperson said.
Two men were treated for injuries at the scene by the London Ambulance Service (LAS) before one was taken to a major trauma centre and the other to hospital.
Conditions have been put in place to prevent serious disorder, stopping protesters from gathering in the area until 13:00 BST on Sunday.
Seven men, whose ages have not yet been given, remained in police custody, the force said.
An eighth was arrested for breaching the order banning protesters from gathering.
The force had earlier said it believed the altercation had involved only pro-monarchy protesters.
The area has been cordoned off while initial investigations take place.
An LAS spokesperson said: “We were called at 09:56 BST today (June 20) to reports of an assault in Princes Gate.
“We sent a number of resources to the scene including ambulance crews, paramedics in fast response cars and our Tactical Response Unit.
“We treated two patients at the scene and took one to hospital and one to a major trauma centre.”
Their injuries were not believed to be life-threatening, they added.
A number of national embassies are located on or near Prince’s Gate, including the Embassy of The Islamic Republic of Iran.
