U.S. House Speaker Nancy Pelosi on Sunday said she plans to appoint additional Republicans, including a staunch Trump critic, to the committee probing the January 6 U.S. Capitol insurrection, amid a fierce partisan showdown over who will serve on the body.

Pelosi's Democrats had sought to create a bipartisan, independent 9/11-style commission to investigate the Capitol insurrection.

Pelosi said that Republicans including Kinzinger, a strong Trump critic and six-term congressman from Illinois, "have expressed an interest to serve on the select committee."

Pelosi herself had already appointed to the committee Republican congresswoman Liz Cheney, who was also among the 10 Republicans who voted to impeach Trump in January.

The first hearing of the commission, which has the power to subpoena witnesses and documents, is scheduled for Tuesday.