Ken Livingstone was angrily accused of being a "Nazi apologist" by Labour MP John Mann, in a confrontation outside the BBC that was caught on camera.
Labour MPs have demanded Livingstone be suspended from Labour for comments about Hitler and antisemitism.
Walking down a flight of stairs at the Milbank studios in Westminster towards Livingstone and jabbing a finger, Mann accused the former London mayor of "rewriting history".
"You’re a lying racist. A Nazi Apologist. You’re a disgusting Nazi apologist, Livingstone," he said. "Go back and check what Hitler did. There is a book called Mein Kampf."
The row began outside the studio, in footage captured by ITV News. Livingstone was speaking to LBC radio at the time. The former London mayor told the station: "I’ve got a violent MP threatening me."
The argument erupted after Livingstone defended Bradford West MP Naz Shah, who yesterday was suspended from Labour for Facebook posts about Israel.
Speaking to BBC Radio London this morning, Livingstone said of Shah: “Her remarks were over the top but she’s not anti-Semitic. I’ve been in the Labour Party for 47 years, I’ve never heard anyone say anything antisemitic.”
He added: "Let’s remember when Hitler won his election in 1932 his policy then was that Jews should be moved to Israel he was supporting Zionism - before he went mad and ended up killing six million Jews."
"There’s been a very well-orchestrated campaign by the Israel lobby to smear anybody who criticised Israeli policy as antisemitic."
In a Facebook post in 2014, before she became MP for Bradford West, Shah shared a graphic which showed an image of Israel’s outline superimposed onto a map of the US under the headline “Solution for Israel-Palestine Conflict - Relocate Israel into United States”, with the comment “problem solved".
The argument between Mann and Livingstone continued on the BBC's Daily Politics programme.
Asked if he thought Livingstone was antisemitic, Mann said: “Yes he is.” And the Labour MP attacked the claim Hitler had supported Jewish people moving to Israel.
"Hitler was not a zionist," Mann said. "Hitler blocked any attempt to get Jews into what was then Palestine."
"I think you’ve lost it Mr Livingstone," he added. "I think you need some help."
Livingstone hit back: "I've not said Hitler was a zionist. What I said was, his policy in 1932 was to depict Germany's Jews to Israel."
Nick Clegg, who was also on the programme, expressed confusion at what Livingstone had said.
"In all my years, I’ve never seen the perverse logic that starts throwing Hitler and a rewriting of history into an incredibly sensitive debate.
"What possessed you to talk about Hitler and your views of his approach to zionism?" the former Lib Dem leader added.