Image copyright Chicago Police Image caption All four suspects have been charged with unlawful restraint and aggravated battery.

Four black people face hate crime and kidnapping charges for the Facebook Live-aired torture of a mentally disabled white man.

Jordan Hill, 18, Tesfaye Cooper, 18, Brittany Covington, 18, and Tanishia Covington, 24, are expected to appear in a Chicago court on Friday.

In the video, the assailants can be heard making derogatory statements against white people and Donald Trump.

Chicago police have described the incident as a "sickening".

The suspects have also all been charged with aggravated unlawful restraint and aggravated battery with a deadly weapon.

Image copyright Facebook Image caption The victim was made to drink from a toilet bowl and had a gag placed over his mouth

Mr Hill is further charged with robbery and possession of a stolen motor.

All the suspects, apart from Tanishia Covington, also each face a count of residential burglary.

In an assault that went on for two days in a flat on the Illinois city's west side, the victim was made to drink from a toilet bowl, had part of his scalp removed with a knife, and was bound, gagged and beaten.

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The unnamed 18-year-old - a school acquaintance of one of the alleged attackers - was found disorientated, walking the streets.

He was taken to hospital, traumatised, and had difficulty communicating with police, but was later discharged.

"It makes you wonder what would make individuals treat somebody like that," said Chicago Police Superintendent Eddie Johnson.

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"I've been a cop for 28 years, and I've seen things that you shouldn't see in a lifetime, but it still amazes me how you still see things that you just shouldn't."

Another police spokesman said earlier that the four black suspects had made "terrible racist statements" during the assault.

But he said investigators suspect the victim was targeted because he has "special needs", not because he is white.

In the 30-minute video, the attackers can be seen cutting the victim's clothes, dropping cigarette ash on him, pushing his head back with a foot and drawing blood by cutting off some of his hair with a knife.

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Several people can be seen drinking, laughing and smoking, while their captive cowers in the corner of the room.

In other videos posted online the young man is beaten, made to drink from a toilet bowl and forced at knife-point to say: "I love black people".

An African-American woman talks to the camera, sometimes with slurred speech. At least two male African-Americans are also visible in the footage.

The incident has provoked a strong reaction on Twitter, especially among the alt-right - the fringe group that celebrated US President-elect Trump's election win with Nazi salutes.

They said the mainstream media was slower to react, and the police more hesitant to label it a hate crime, than if a black person had been assaulted by white people.

The hashtag #BLMKidnapping was adopted by users suggesting the Black Lives Matter campaign was in some way involved.

But police have not mentioned the organisation in connection with the incident.