Ex-Seinfeld star Michael Richards has apologised for directing a racist insult at a heckler during a stand-up comedy performance in Los Angeles.
The 57-year-old, who played eccentric neighbour Cosmo Kramer in the long-running sitcom, said he "went into a rage" when his act was interrupted.
"I'm really busted up over this and I'm very, very sorry," Richards said.
His former co-star Jerry Seinfeld said he felt "sick" about what he branded a "horrible, horrible mistake".
"It is so extremely offensive. I feel terrible for all the people who have been hurt," Seinfeld added.
Richards had been performing at the Laugh Factory on Friday when two black audience members appeared to shout at him that he was not funny.
He paced across the stage in a fury and repeatedly taunted the men for disrupting his routine.
While some people in the crowd were heard to chuckle, another was audibly horrified.
Richards' performance was captured on video and passed to TMZ
The events were captured on video and passed to the TMZ.com entertainment website.
In a statement, Richards said: "I was at the comedy club trying to do my act and got heckled. I took it badly and went into a rage."
He apologised to "those people in the audience - the blacks, the Hispanics and the whites, everybody who was there and took the brunt of that anger and hate and rage, and how it came through".
Seinfeld was not the only member of the entertainment industry to condemn Richards.
Veteran publicist Michael Levine said the remarks were inexcusable.
"I've never seen anything like this in my life," he said. "I think it's a career-ruiner for him."
Comedian Paul Rodriguez, who co-owns the Laugh Factory, said he had banned the performer from the well-known venue.
"It was unfortunate, it was sad," he said.
"I was at the back watching this, and I kept waiting for a punchline that could justify the words before it. It didn't come."