WASHINGTON - Hours after hundreds of President Donald Trump's supporters stormed the U.S. Capitol in a harrowing assault on American democracy, a shaken Congress on Thursday formally certified Democrat Joe Biden’s election victory.

Late on Wednesday houses of Congress resumed their work on certifying Biden's Electoral College win, with debate stretching into the early hours of Thursday. After debate, the Senate and the House of Representatives rejected two objections to the tally and certified the final Electoral College vote with Biden receiving 306 votes and Trump 232 votes.

Vice President Mike Pence, in declaring the final vote totals behind Biden's victory, said this "shall be deemed a sufficient declaration of the persons elected president and vice president of the United States."

The outcome had never been in doubt, but had been interrupted by rioters – spurred on by Trump – who forced their way past metal security barricades, broke windows and scaled walls to fight their way into the Capitol.

Police said four people died during the chaos - one from gunshot wounds and three from medical emergencies - and 52 people were arrested.

Some besieged the House of Representatives chamber while lawmakers were inside, banging on its doors and forcing suspension of the certification debate. Security officers piled furniture against the chamber's door and drew their pistols before helping lawmakers and others escape.

The assault on the Capitol was the culmination of months of divisive and escalating rhetoric around the Nov. 3 election, with the Republican president repeatedly making false claims that the vote was rigged and urging his supporters to help him overturn his loss.

The chaos unfolded after Trump - who before the election refused to commit to a peaceful transfer of power if he lost - addressed thousands of supporters near the White House and told them to march on the Capitol to express their anger at the voting process.

He told his supporters to pressure their elected officials to reject the results, urging them "to fight." 

Some prominent Republicans in Congress strongly criticized Trump, putting the blame for the day’s violence squarely on his shoulders.

"There is no question that the President formed the mob, the President incited the mob, the President addressed the mob. He lit the flame," House Republican Conference Chairwoman Liz Cheney said on Twitter.

Republican Senator Tom Cotton, a leading conservative from Arkansas, called on Trump to accept his election loss and "quit misleading the American people and repudiate mob violence."

Biden and Vice President-elect Kamala Harris are due to take office on Jan. 20.

(Reporting by Patricia Zengerle and Jonathan Landay Additional reporting by Daphne Psaledakis, Lisa Lambert, Mark Hosenball, Doina Chiacu, Jonathan Allen, Susan Cornwell, Susan Heavey, Richard Cowan, Tim Ahmann, David Shepardson and Diane Bartz Writing by Andy Sullivan, John Whitesides and James Oliphant; Editing by Ross Colvin, Peter Cooney, William Mallard and Frances Kerry) ((frances.kerry@thomsonreuters.com; +44 207 542 6136; Reuters Messaging: frances.kerry.thomsonreuters.com@reuters.net))