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 programme, said in a pre-recorded statement played on radio today.

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

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

Howson caused outrage yesterday for attacking Christine Assange's decision to cancel a pre-planned phone interview due to his treatment of a previous guest.

"I won't be doing an interview with you because you're acting like a pig," said the mother of the WikiLeaks website founder.

Howson responded by screaming on air, "Sieg Heil, Sieg Heil, Sieg Heil" as Ms Assange hung up the phone.

He later said he was pointing out the "Nazi mentality" of those who tried to censor him.

But station managers for 3AW, owned by Fairfax Media, emerged from closed-door meetings on Monday to announce Howson's four-week sabbatical and play his pre-recorded apology.

"I understand that many listeners took offence to these comments and I sincerely regret having uttered them," Howson said in the recording.

"I did not intend to imply that our guests or anyone shares the views of the Nazi party or seeks to control free speech and I again offer my sincere apologies."

Last year, Howson caused similar offence for verbally abusing a young radio producer and a co-host on air.

- AAP