(CNN) -- Justin Bieber was in serious damage control mode Sunday after a video of him telling a racist joke to friends surfaced.
In the video, posted to TMZ.com, the pop star, then 15, asks: "Why are black people afraid of chain saws?"
He answers his own question: "Run n*****, n*****, n*****, n*****," he says, imitating the sound of a chain saw. Then he laughs.
TMZ reported it got the video four years ago but decided against posting it then because of Bieber's age and because he "immediately told his friends what he did was stupid." It was reportedly shot backstage at a promotional event.
"As a young man, I didn't understand the power of certain words and how they can hurt. I thought it was OK to repeat hurtful words and jokes, but didn't realize at the time that it wasn't funny and that in fact my actions were continuing the ignorance," Bieber, now 20, said in a statement.
He added: "I take my friendships with people of all cultures very seriously and I apologize for offending or hurting anyone with my childish and inexcusable mistake. I was a kid then and I am a man now who knows my responsibility to the world and to not make that mistake again."
The video is the latest in a string of troubles for the star, who shot to fame as a fresh-faced teen.
There was a DUI arrest in Miami, an assault charge in Toronto and a felony vandalism probe in Los Angeles.
Also, the Federal Aviation Administration is investigating allegations that Bieber and other passengers aboard a charter flight from Canada to New Jersey's Teterboro Airport interfered with the flight crew.
None of the criminal charges that Bieber faces appear to threaten his freedom. Probation sentences, fines, community service and counseling are routinely given in such cases.
CNN's Ed Payne and Michael Martinez contributed to this report.