CHICAGO - Racial issues in the United States have once again been thrust into the international media spotlight this week, with a live Facebook video circulated online showing a group of young African-Americans brutally tortured a mentally disabled white man while shouting anti-white messages and insulting US President-elect Donald Trump.

The four people who the Chicago police said had participated in the assault were charged with hate crimes on Thursday.

The video of the beating lasts about 30 minutes and shows the victim, who the police said had "mental health challenges," cowered in a corner with his hands bound with orange cords and his mouth covered with tape.

In the live stream, the assailants cut the 18-year-old victim's scalp with a knife and yelled obscenities about Donald Trump and "white people" while kicking and hitting him. At one point, they made the victim drink from a toilet.

The beating that revealed bare racial tensions in the country has sparkled massive outrage and deep concerns on the country's painful racial split.

US President Barack Obama described the Facebook Live attack as a "despicable sort" of hate crime while interviewed by a Chicago-area television station on Thursday.

The president said that while he did not believe US race relations had worsened, public exposure to race crimes had grown in the digital age.

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

In Chicago, Police Superintendent Eddie Johnson called the assault "sickening," adding that "It makes you wonder what would make individuals treat somebody like that."

Police said all four suspects have given statements admitting to their roles in the alleged attack. They are scheduled to appear in bond court Friday.

The victim, whom the police did not name, was hospitalized for undisclosed injuries.