UPDATE: Three teenagers were arrested on Tuesday afternoon after the video depicting the assault was downloaded and viewed by police officers.
Kent Police told HuffPost UK: "Two 16-year-old girls were arrested this afternoon on suspicion of assault. A 15-year-old was also arrested on suspicion of aiding and abetting an assault. They are all currently in police custody awaiting interview."
An attack on a 15-year old filmed for social sharing app SnapChat has been uploaded to Facebook by the victim's mother.
Police are now investigating the assault as actual bodily harm after the short clip was obtained by the mum last week.
Police confirmed that the victim suffered a black eye.
In a post on Facebook, Sarah Niven spoke of the horror at finding out her daughter had been victim to the vicious attack - only to suffer further humiliation online.
Two girls set about beating the victim and even set fire to her hair extensions.
She wrote: "These two girls one aged 18 had beaten up my 15 year old daughter and filmed it!
"Humiliating her by burning her hair extensions and laughing about it on SnapChat!
Kent Police say that they are now launching an investigation into the incident after officers viewed the clip online.
A Kent Police spokesperson told HuffPost UK: "Police are investigating an assault which is reported to have occurred in Hesketh Park, Park Road, Dartford between 5pm and 6pm on 11 July 2015.
"It is alleged that a 15-year-old girl was assaulted. The girl is reported to have suffered a black eye.
"Officers are aware of a video, reportedly taken of the incident, circulating on social network sites. This has been viewed and downloaded by detectives.
"Enquiries are on-going at this stage."
Last week, a teenage bully filmed forcing two girls to their knees was forced to flee her home in Birmingham after it was vandalised by an angry mob.