A Melbourne radio host who taunted Julian Assange's mother with a Nazi slogan has apologised and been taken off air for a month.

"I unreservedly apologise," John-Michael Howson, co-host of 3AW's Sunday Morning program, said in a pre-recorded statement played on radio today.

The veteran entertainment reporter has been removed from hosting the weekend show for four weeks, the station says.

"This was completely unacceptable behaviour and we don't condone it at all,’’ said station manager Shane Healy.