WASHINGTON: US House Speaker Nancy Pelosi on Sunday named an outspoken Republican critic of former president Donald Trump to join the committee probing the January 6 US Capitol insurrection, two days ahead of its first hearings.

The top Democrat in Congress announced the appointment of Representative Adam Kinzinger, who voted to impeach Trump over the riot, in a statement hailing the "great patriotism" he would bring to the panel's mission "to find the facts and protect our democracy."

Hundreds of Trump's supporters, many associated with ultra-nationalist and white supremacist groups, stormed the US legislature six months ago to halt President Joe Biden's confirmation. They had been egged on by Trump, whose fiery speech earlier that day falsely claiming election fraud was the culmination of months of baseless claims about a contest he lost fairly to Biden.

A comfortable majority of 57 senators - including seven from his own party - voted to convict Trump after he was impeached by the House for inciting the riot, although this fell short of the two-thirds majority required under Senate rules to unseat a president.

"Let me be clear, I'm a Republican dedicated to conservative values, but I swore an oath to uphold and defend the Constitution. And while this is not the position I expected to be in or sought out, when duty calls, I will always answer," Kinzinger said in a statement.

"This moment requires a serious, clear-eyed, non-partisan approach. We are duty-bound to conduct a full investigation on the worst attack on the Capitol since 1814 and to make sure it can never happen again."