Police in Lambeth are appealing for witnesses and information after a man was seriously injured in one of a number of incidents along the South Bank.
Officers were called at 1.50am last Saturday to reports of a 21-year-old man suffering head and facial injuries in the York Road area.
The man told police he had been the victim of an assault after being attacked by a group of up to 12 males and females at the location.
The victim had been walking near the Shell Centre when he was approached by the group who attacked him.
The man was taken to hospital for treatment.
Officers are also investigating a nearby incident in which a 25-year-old man was attacked by a similar group at around 4.30am on Saturday.
The victim ran off and alerted police. He did not require hospital treatment.
A 14-year-old female and a 15-year-old male have been arrested on suspicion of grievous bodily harm and actual bodily harm in relation to the these incidents.
Both have been released on bail pending further inquiries.
Lambeth Police say that subsequent investigations have revealed that there were a number of incidents in the South Bank area between Hungerford Bridge and Westminster Bridge from the evening of Friday 21 October into the early hours of Saturday 22 October.
None of these incidents resulted in any significant injuries.
"I am appealing to anyone who was in the area and witnessed a group of up to 20 males and females, aged between 14 and 18, acting in an aggressive manner between approximately 11.3pm on Friday 21 October until around 4.30am the following morning," said Detective Constable Natasha Swan of Lambeth CID.
"So far we are only aware of the one incident which resulted in serious injury but it is apparent this group intimidated and threatened people with their behaviour over a significant period of time.
"If you witnessed this group, or are a victim yourself, please contact us."
Anyone with information is asked to contact Lambeth CID via 101 or call Crimestoppers anonymously on 0800 555 111.