Richards has said he is "really busted up" over the incident

Speaking on the Rev Jesse Jackson's Keep Hope Alive show, Richards said he had never used racist language and it was provoked by "humiliation".

His publicist Howard Rubenstein said he has started anger management therapy.

The two men who were verbally attacked for heckling Richards' comedy show have demanded a face-to-face apology.

Richards said on air that he attempted to find Frank McBride and Kyle Doss, but they had left the venue and have since proved difficult to locate.

'Racial wound'

"I've tried to meet them, to talk to them, to get some healing," said Richards, who played Seinfeld's neighbour Kramer in the US TV sitcom.

"The way it came through me was like a freight train," he added of his tirade.

"He acknowledged that his statements were harmful and opened a terrible racial wound in our nation," said Mr Rubenstein.

Richards (r) played the eccentric Cosmo Kramer in Seinfeld

"He pledges never ever to say anything like that again. He's quite remorseful."

Rev Jackson, who condemned the outburst as "hateful" and "sick", said Richards' appearance on his programme created an opportunity for a wider discussion about "cultural isolation" in the entertainment industry.

"We might turn this minus into a plus," he said.

Richards has already publicly apologised for the incident on the Late Show with David Letterman.

Mr McBride and Mr Doss's lawyer, Gloria Allred, said it was "not enough" to say sorry on the programme, suggesting that monetary compensation should be considered.