Nancy Pelosi, chairwoman of the US House of Representatives, has turned down two Republican nominees to serve on the Committee to Investigate the January 6th attack on the Capitol.
Out of respect for the integrity of the investigation and concern about the statements and actions of these MPs, they must reject Jim Banks and Jim Jordan as members of the panel, Pelosi said on Wednesday.
She had to approve the nomination of the nominees.
The Republican minority leader in the Chamber of Congress, Kevin McCarthy, threatened that the Republicans would boycott the committee and accused Pelosi of "abuse of power".
After a violent dispute over the committee in the US House of Representatives, McCarthy finally nominated five candidates for the body on Monday.
They are all considered supporters of former Republican President Donald Trump.
Jordan is one of the most ardent Trump supporters.
After his nomination, Banks had declared that the panel should not only investigate the attack on the Capitol on January 6th, but also "hundreds of violent political riots last summer", for example by "left-wing extremists".
Pelosi fears that the appointment of Jordan and Banks could affect the integrity of the investigation.
A full investigation is needed into who organized this attack on the Capitol and who paid for it, Pelosi said.
The committee's first hearing is scheduled for next week.
Members of the police force, the Capitol and police officers of the capital Washington are to be heard.
The committee is to investigate the background to the attack on the Capitol.
Supporters of Trump stormed the seat of the US Congress in Washington on January 6th.
Five people were killed, including a police officer.