The US Congress has certified Joe Biden's victory in the presidential election, hours after Trump supporters stormed the building in an attack that saw four people die. Lawmakers resumed the session after police managed to remove the mob, which had been encouraged by President Donald Trump in a bid to overturn his defeat. The certification clears the way for Mr Biden to be sworn in on 20 January. In response, Mr Trump finally pledged an "orderly transition" of power. Democrat Joe Biden's victory was confirmed at about 03:30 local time (08:30 GMT) on Thursday by a joint session presided over by Vice-President Mike Pence, who said the violence had been a "dark day in the history of the United States Capitol".Wednesday's chaotic scenes followed months of escalating rhetoric from Mr Trump and some Republican allies that sought to undermine the result of the 3 November election. The invasion of the Capitol by the president's supporters some armed was an event without precedent in modern American history. Mr Biden blasted the "insurrection" as Mr Trump while telling the mob to "go home", continued to make false claims of electoral fraud. The outgoing president's Twitter and Facebook accounts were later frozen. After objections by some Republican lawmakers to overturn the result in Arizona and Pennsylvania were rejected, Congress formally certified the final electoral college vote with Mr Biden receiving 306 votes to Mr Trump's 232. Shortly afterwards Mr Trump whose social media accounts remain blocked said in a statement: "Even though I totally disagree with the outcome of the election, and the facts bear me out, nevertheless, there will be an orderly transition on January 20th." Meanwhile, Washington DC Mayor Muriel Bowser said one of the four dead a woman was part of a group that forced entry into the House room while it was still in session. They were confronted by plainclothes officers, and an officer pulled out a weapon and fired it. The woman was taken to hospital and later proclaimed dead. She has not been officially named, but local media identified her as San Diego-area US Air Force veteran and Trump supporter Ashli Babbit. One woman and two men died as a result of "medical emergencies", officials said, without giving details. At least 14 members of the police were injured during the unrest. The rampage came as two Democrats won Senate seats in elections in Georgia, which shifted the balance of Congress to their party's effective political control. This major political victory will ease the passage of Mr Biden's agenda after he is inaugurated.