US President Joe Biden was caught on a live microphone Monday calling a Fox News journalist a "stupid son of a b**h" on the sidelines of a White House photo op, AFP reported.

The incident occurred as journalists were leaving the room after the event. Peter Doocy, a reporter from Fox News asked whether inflation is a political liability.

Biden, possibly unaware that his microphone was still on, began by deadpanning, "It's a great asset. More inflation."

He then muttered, "What a stupid son of a b**h."

A pool reporter who was in the room at the time admitted to not being able to hear what Biden actually said over the noise.

Doocy shrugged the insult off in a later interview on Fox, saying, "Yeah, nobody has fact-checked him yet and said it's not true."

Biden has had several run ins with reporters in his year in office. Last June, Biden snapped at CNN reporter Kaitlan Collins for asking, "Why are you so confident (Putin) will change his behavior, Mr. President?”

Biden turned back and responded, “I’m not confident I’m going to change his behavior. What the hell? What do you do all the time?”

The President later apologized for the incident.

In August, Biden sparred with a reporter who asked him questions about the controversial US withdrawal Afghanistan.

In October, the President did not take well to a reporter asking him why he wasn't able to “unite the party.”