Chicago gangs
Jim Allen, a self-described member of the Vice Lords gang speaks with reporters following a press conference in Chicago, Illinois, 2010 Scott Olson/ Getty Images

Three different street gangs in Chicago have reportedly formed an alliance in order to kill police officers in the city following the death of 18-year-old Paul O'Neal.

Chicago police fired shots at the stolen car O'Neal was driving before he crashed into a police vehicle, with shots fired at the unarmed teenager as he attempted to flee the scene, prompting three West Side gangs to make a deadly pact to shoot police officers in 'revenge' for the killing.

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The Vice Lords, Four Corners Hustlers and Black Disciples reportedly sent representatives to a meeting in which it was agreed the Four Corners Hustlers would supply the other gangs with weapons in order to carry out attacks on law enforcement, according to a Police memo, the Chicago Sun Times reported.

The teaming up of the three gangs is unusual, not least because the Black Disciples are a part of the Folk Nation set of gangs in the city, which rivals People Nation, which Vice Lords and Four Corners Hustlers are a part of.

It is not clear what response the authorities have taken to the warning, as in an email to the newspaper a spokesperson for Chicago Police Department said: "To safeguard the integrity of operations, the department does not comment on any security measures."

The shooting of O'Neal, who was fatally injured on 28 July, has prompted mass protests in the city, particularly following the release of footage from six officers' body cameras which show the moments leading up to the shooting – with no camera footage from the officer who fired the fatal shot.

The footage was released just last week, with Sharon Fairley, head of the Independent Police Review Authority that released the videos describing them as "shocking and disturbing", particularly regarding insults flung at the teen as he lies in the street.

Three police officers have been suspended following the incident and the O'Neal family has filed a lawsuit against the officers, with authorities warning the camera footage might provoke retaliation against officers in the city.