A group of suspected Islamists have attacked a meeting of George Galloway's Respect party in Bethnal Green and Bow.
Mr Galloway is trying to attract Muslim voters
Police said there were reports 20 to 30 Asian men had disrupted the meeting and there had then been a fracas outside.
Respect said the men had threatened Mr Galloway's life and talked of a fatwa. After the meeting a man was knocked to the ground and police arrested three.
The anti-war campaigner is standing against Labour loyalist Oona King in the east London constituency.
Ms King's campaign have revealed her car was attacked over the weekend and pelted with eggs.
The alleged attack on Mr Galloway's meeting at about 2100 BST on Tuesday on the Osier estate comes during an already bitter campaign, and hours after a Muslim Council of Britain event was also disrupted.
Oona King's car was covered in eggs
Mr Galloway, a fervent opponent of the war in Iraq, is trying to unseat Ms King, who supported military action.
A Respect spokesman said: "He was very severely threatened, although he wasn't hurt.
"They came in, blocked the door behind them and told George he had a fatwa against him and that he would be hanged."
Mr Galloway was then whisked away to a nearby car by his son-in-law, the spokesman said.
It is understood that one person was knocked down in the fracas and treated in hospital for head injuries.
Meanwhile, a spokesman for Oona King said the candidate had been shouted at by a large group of Bengali youths wearing Respect badges or stickers while campaigning on an estate in the constituency on Saturday.
Kester Dean said: "They were shouting 'Bush and Blair murderers' and 'get out of our estate'. The car was covered in eggs."
He blamed the attack on the "poisonous atmosphere" generated in the campaign so far.
The Respect spokesman said it was not clear if the youths were Respect supporters as the badges were widely available.
"It is behaviour that we absolutely don't want to see."