The Labour candidate selected to contest the crunch Stoke Central by-election battle claimed Jeremy Corbyn was an “IRA supporting friend of Hamas”.
Cllr Gareth Snell made the comments on Twitter as the party’s leadership contest between Mr Corbyn and Owen Smith was in full swing in July last year.
Mr Snell said: “If we have to prefix (Owen) Smith with ‘Pfizer lobbyist’, can we also say ‘IRA supporting friend of Hamas career politician’ Jeremy Corbyn?”
A spokeswoman for Mr Corbyn on Thursday refused to say whether he had been aware of the tweets.
“We won’t comment on this,” the spokeswoman said.
Mr Snell will attempt to hold the Stoke-on-Trent Central seat for Labour next month.
He is taking on Ukip leader Paul Nuttall, who will hope to capitalise on a strong Brexit vote in last year’s EU referendum and secure himself a place in the Commons.
Borough councillor Mr Snell - standing for the seat in a city where overall almost 70% voted for Leave - also once tweeted that Brexit was a “massive pile of s**t”.
The by-election was triggered after Tristram Hunt announced he would be stepping down to become director of the Victoria and Albert Museum.
In a series of tweets on July 19, Mr Snell said: “We doing hyberbole? If so, it’s a choice between IRA supporting friend of Hamas career politician Corbyn vs Smith.”
He also said: “Smith learnt politics in the heat of the fight in South Wales. Corbyn sipped tea in trendy north London with career politician and Viscount.”
Later, Mr Snell added: “For clarity, my previous comments were to demonstrate the absurdity of the hyperbole I’ve read in the last two hours.”
Mr Corbyn won the leadership contest on September 24 last year.
In a separate tweet, on September 29 2016, Mr Snell said: “Soft Brexit, Hard Brexit, massive pile of s**t. Sloppy Brexit, messy Brexit, quit, quit, quit.”
Meanwhile, the Conservatives selected project manager Trudy Harrison to take on Labour in the Copeland by-election.
The two contests on February 23 will present a headache for Mr Corbyn, with strong challenges in both seats.
In the 2015 general election, Mr Hunt had a 5,179 majority over Ukip .
In Copeland Ms Harrison will attempt to win the seat from Labour after Jamie Reed quit to take up a position at the Sellafield power plant.