Mitch McConnell has lashed out at the “loony lies and conspiracy theories” promoted by Georgia congresswoman Marjorie Taylor Greene, an ardent supporter of former president Donald Trump, as a “cancer” on the party.

The comments from the top Republican in the US Senate reflect the intensifying conflict that has broken out within the party since it lost the White House and both chambers of Congress, as well as the fallout from the January 6 attack on the US Capitol.

Ms Greene, 46, is a first-term member of the US House of Representatives and has become a lightning rod for criticism because of her promotion of QAnon, a far-right extremist ideology based on a series of false claims. She has also tried to overturn the results of the November presidential election.

Ms Greene has also faced a backlash for retweeting endorsements of political violence, including the execution of Democratic lawmakers and FBI agents, before she ran for office.

“Somebody who’s suggested that perhaps no airplane hit the Pentagon on 9/11, that horrifying school shootings were pre-staged, and that the Clintons crashed JFK Jr’s airplane is not living in reality,” Mr McConnell said in a statement to The Hill newspaper.

“This has nothing to do with the challenges facing American families or the robust debates on substance that can strengthen our party.”

Mr McConnell’s comments came as Ms Greene was facing action by Democrats who control the House to strip her of her committee assignments in response to her views, with some feeling physically threatened by the lawmaker’s presence and her supporters.

Cori Bush, a Democratic lawmaker from Missouri, said she was forced to move her office away from Ms Greene’s after an altercation over mask-wearing with the congresswoman.

Alexandria Ocasio-Cortez, the Democratic lawmaker from New York, has also expressed concern over safety in Congress following the January 6 attacks.

She offered a harrowing account of the Capitol assault on Instagram Live on Monday. “I hear these huge violent bangs on my door and then every door going into my office,” she said. “It felt like a zombie movie.”

Mr McConnell’s forceful rebuttal of Ms Greene stands in contrast to the approach taken by Kevin McCarthy, the top Republican in the House, who met Mr Trump last week at his Mar-a-Lago resort in Florida and is due to discuss the Congresswoman’s fate with her this week.

Ms Greene has remained defiant despite the mounting criticism. “The real cancer for the Republican party is weak Republicans who only know how to lose gracefully,” she said on Twitter in response to Mr McConnell’s comments. “This is why we are losing our country.”

Mr McConnell also defended Liz Cheney, the member of the House from Wyoming and third-ranking Republican in the chamber, who voted to impeach Mr Trump for inciting the assault on the Capitol. Ms Cheney has faced calls to be removed from party leadership for defying the former president.

“Liz Cheney is a leader with deep convictions and the courage to act on them. She is an important leader in our party and in our nation,” Mr McConnell said.