The Democratic leadership of the US House of Representatives has urged an investigation into a video shared by a Republican lawmaker that depicted him swinging swords at US President Joe Biden and killing his Democratic colleague.

Nancy Pelosi, Speaker of the United States House of Representatives, said the threats to US lawmakers and the president "shouldn't be tolerated."

Republican congressman Paul Gosar, who shared the video, said in a statement that he will always fight for the rule of law, securing the border and defending America's first agenda.

The Arizona Republican is a staunch ally of former President Donald Trump who has backed his election fraud claims and called January 6 rioters as "peaceful patriots."

Twitter flagged the video and restricted engagement with the tweet. Later, the video was deleted and Gosar posted a meme saying that it was a "cartoon" and people should "relax."

Call for resignation

The White House condemned the video, while other Democrats called for Gosar to leave office.

Another Democrat, Ted Lieu, said in a tweet of his own: “In any workplace in America, if a coworker made an anime video killing another coworker, that person would be fired.”

A House Ethics Committee staff official declined to comment.

One ethics expert said that threatening behaviour could violate both House ethics rules and federal criminal statutes.

"He is putting his real feelings out there, and his real feelings look very threatening," said Craig Holman, ethics lobbyist for Public Citizen.