Senate Republican leader Mitch McConnell has said the mob that stormed the Capitol was "fed lies" by US President Donald Trump.
Mr McConnell's remarks in opening the Senate on Tuesday are his most severe and public rebuke of Mr Trump.
The Republican leader vowed a "safe and successful" inauguration of US President-elect Joe Biden on Wednesday at the Capitol, which is under extremely tight security.
Mr McConnell said: "The mob was fed lies. They were provoked by the president and other powerful people, and they tried to use fear and violence to stop a specific proceeding of branch of the federal government."
Mr McConnell said "we'll move forward" after Mr Biden's inauguration on the Capitol's West Front – what he noted former president George HW Bush has called "democracy's front porch".
Mr Trump's last full day in office is also senators' first day back since the deadly Capitol siege, an unparalleled time of transition as the Senate presses ahead to his impeachment trial and starts confirmation hearings on Mr Biden's cabinet.
Three new Democratic senators-elect are set to be sworn into office shortly after Mr Biden's inauguration at the Capitol, which is under extreme security since the bloody pro-Trump riot. The new senators' arrival will give the Democrats the most slim majority, a 50-50 divided Senate chamber, with the new vice president, Kamala Harris, swearing them in and serving as an eventual tie-breaking vote.
Mr McConnell and Senate Democratic leader Chuck Schumer are set to confer about the arrangements ahead.
The start of the new session of Congress will force senators to come to terms with the post-Trump era, a transfer of power like almost none other in the nation's history. Senators are returning to a Capitol shattered from the riot, but also a Senate ground to a halt by Congress members' own extreme partisanship.
Republican senators, in particular, face a daunting choice of whether to convict Mr Trump of inciting the insurrection, the first impeachment trial of a president no longer in office, in a break with the defeated president who continues to hold great sway over the party but whose future is uncertain.
Senators are also being asked to start confirming Mr Biden's cabinet nominees and consider passage of a sweeping new 1.9 trillion dollar Covid-19 relief bill.
In opening remarks at his confirmation hearing, Mr Biden's nominee for secretary of the Department of Homeland Security, Alejandro Mayorkas, vowed to get to the bottom of the "horrifying" attack on the Capitol.
Mr Mayorkas told the Senate Homeland Security Committee that if confirmed he would do everything possible to ensure "the desecration of the building that stands as one of the three pillars of our democracy, and the terror felt by you, your colleagues, staff, and everyone present, will not happen again".
Five of Mr Biden's nominees are set for hearings on Tuesday as the Senate prepares for swift confirmation of some as soon as the president-elect takes office, as is often done on Inauguration Day, particularly for the White House's national security team.