Democrat presidential hopeful Elizabeth Warren rejected a handshake from rival Bernie Sanders after the pair clashed in a TV debate over whether a woman could become US president.
The non-aggression pact between the party’s two most Left-leaning candidates was in tatters following the confrontation, the final debate before voting on nominations starts next month.
At the end of the session, Ms Warren walked over to Mr Sanders, who held out his right hand as if for her to shake it.
She instead clasped her hands together and began to address the rival senator.
What appeared to be a confrontational exchange then occurred – though their comments were inaudible – before fellow candidate Tom Steyer came between and the two split away from each other.
It comes after Ms Warren claimed Mr Sanders “disagreed” that a woman could be elected as US president in 2020.
Ms Warren, in a statement released on Monday, said: "Among the topics that came up was what would happen if Democrats nominated a female candidate.
"I thought a woman could win; he disagreed."
Mr Sanders has strenuously denied the accusation, and did so again in the debate.
He said it was "incomprehensible" he could have expressed this view, while Ms Warren confirmed the comment and said she disagreed with Mr Sanders.
She said: "Bernie is my friend and I am not here to try to fight with Bernie.
"But look, this question about whether or not a woman can be president has been raised and it’s time for us to attack it head-on.”
There are just three weeks until first nominating contest in Iowa, with 12 candidates still vying for the spot.
Opinion polls show the top four contenders are former Vice President Joe Biden, Mr Sanders, Ms Warren, and former mayor of South Bend, Indiana, Pete Buttigieg.
