President Obama has denounced a Facebook Live video of black youths in Chicago tying up and torturing a white mentally disabled man as 'despicable' but denied that race relations in the US are getting worse.

The video, which apparently showed four youths aged 18-24 beating, cutting and laughing at the bound and gagged man, was streamed on Tuesday by one of those arrested.

But, the President - who has a home in the affluent Hyde Park suburb of Chicago - told CBS, this was not a sign of a worsening racial divide.

Obama - the junior senator for Illinois before he became president - said it was just an example of social media revealing problems that have always been there.

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Hopeful: President Obama said that though four black youths were seen on camera apparently torturing a white man in an alleged hate crime, he was still hopeful America's race relations

Torture: The disabled man is bound and beaten on the video. Obama said this was just a case of social media making it easier to see the racial divide that has always existed

'I don't think it's accurate to say race relations are getting worse,' he told host Jay Levine, saying things were also difficult in Chicago in the mid-1980s, when a block of white councilmen deliberately scuppered all proposals by a black mayor.

'In part because we see visuals of racial tensions, violence and so forth because of smart phones and the Internet,' the president said.

'What we have seen as surfacing, I think, are a lot of problems that have been there a long time.

'Whether it's tensions between police and communities, whether it's hate crimes of the despicable sort that has just now recently surfaced on Facebook.'

Cut: The man was pictured being cut on the head with a knife (circled, left). Obama believes that the future generations of Americans have 'smarter, better' ideas of race relations

He added: 'The good news is that the next generation that's coming behind us … have smarter, better, more thoughtful attitudes about race.

'I think the overall trajectory of race relations in this country is actually very positive. It doesn't mean that all racial problems have gone away. It means that we have the capacity to get better.'

Chicago police announced Wednesday that three 18-year-olds and a 24-year-old - two of them girls - had been arrested in relation to the video.

The victim was a white man in his teens or early twenties. All of the suspects are black.

Arrested: Brittany Covington (left) and Tesfaye Cooper (right), both 18, were arrested Wed. Police say they were two of the four suspects accused of hate crimes, among others

Charged: Jordan Hill (left), 18, and Tanisha Covinton (right), 24, were also charged with hate crimes. In the video someone can be heard saying 'f**k Trump' and 'f**k white people'

They filmed themselves kicking and punching the bound and gagged man, and cutting his hair until his scalp bled. They also made him drink water from a toilet.

Someone can be heard in the footage yelling 'f**k Donald Trump. F**k white people' while the two men express their hopes that the video will go viral.

The youths have been identified as Jordan Hill, 18; Tesfaye Cooper, 18; and sisters Brittany and Tanisha Covington, who are 18 and 24, respectively.

They were arrested Wednesday. The victim had escaped and was helped after being seen wandering in a Chicago street.

All four suspects face charges of aggravated kidnapping, aggravated unlawful restraint, aggravated battery and a hate crime.

Hill, who was acquainted with the victim, faces an additional charge of robbery and possession of a stolen vehicle.