Bernie Sanders was forced to step in to prevent a fist fight during a heated war of words at a US Senate hearing.

The experienced senator played peacekeeper after Republican senator Markwayne Mullin, a former-cage-fighter-turned-politician, took to his feet to confront union chief Sean O’Brien.

Moments earlier, Mr Mullin branded Mr O’Brien, the president of the International Brotherhood of Teamsters, a “moron” and challenged him to “stand your butt up”.

Mr Sanders yelled at Mr Mullin to sit down, banged his gavel several times and told both to stop their row.

“You are a United States senator!” Mr Sanders yelled at Mr Mullin.

“This is a hearing, and God knows the American people have enough contempt for Congress, let’s not make it worse.”

While the pair never came face to face, they shouted for around six minutes as Mr Sanders tried to regain order of the Senate hearing.

The two appeared to conclude their exchange by agreeing to have coffee together.

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The exchange occurred after Oklahoma senator, Mr Mullin, recalled an interaction he had with Mr O’Brien in June on social media platform X, formerly known as Twitter.

At the time, the pair discussed engaging in an MMA fight for charity.

Mr Mullin read aloud Mr O’Brien’s original set of tweets during the hearing on Tuesday, which said: “Greedy CEO who pretends like he’s self-made.

“In reality, just a clown and a fraud. Always has been, always will be. Quit the tough guy act in these senate hearings. You know where to find me. Any place, anytime, cowboy.”

After reading out the post, Mr Mullin said the pair could “finish it here”, before calling on Mr O’Brien to “stand your butt up”.

“You stand your butt up,” replied Mr O’Brien, before Mr Sanders intervened.