America's president-elect has condemned Donald Trump's behaviour and called those who stormed the US Capitol "domestic terrorists".
Joe Biden said Wednesday's astonishing scenes were an "assault on our liberty".
Of the demonstrators, he said: "Don't dare call them protesters - they were a riotous mob, insurrectionists."
Turning to Mr Trump, he said the president had "unleashed an all-out assault on our institutions of democracy - and yesterday was the culmination", adding that US presidents are not above the law.
Mr Biden, who will be inaugurated on 20 January, said it had been one of the darkest days in US history - a result of Mr Trump's "unrelenting attack on democracy".
Black Lives Matter protesters would have been treated differently if they had gathered at the Capitol, the president-elect said.
Speaking shortly afterwards, House Speaker Nancy Pelosi said Donald Trump had "incited an armed insurrection against America", describing him as a "very dangerous person who should not continue in office".
He had called for a "seditious act" and was "deadly" to Americans and US democracy, committing an "unspeakable assault on our nation and our people", Ms Pelosi said.
The scenes witnessed on Wednesday, which she described as a "gleeful desecration", were "horrors that will forever stain our nation's history, instigated by the president of the United States".
Ms Pelosi described those who forced their way into the US Capitol as "terrorists". Four people died during the chaos, including US Air Force veteran Ashli Babbitt.
Images showed security forces with their guns drawn inside the chamber of the House of Representatives.
Politicians scrambled to grab gas masks from under their seats after being ordered to drop to the floor for their safety.
"We are in a very difficult place in our country as long as Donald Trump sits in the White House," said Ms Pelosi.
While praising officers who "acted so bravely and with such concern", she said there had been "a failure at the top of the Capitol Police".
One of the protesters entered her office and put his feet up on her desk. Other members' offices were ransacked, and threatening messages were left behind.
Ms Pelosi called for Mr Trump to be removed from office immediately, and said the Democrats were pushing for his impeachment.
The veteran Democratic politician said she was expecting a quick decision from Vice President Mike Pence about whether to invoke the 25th amendment in seeking to remove Mr Trump from the White House.
Senate Democratic Leader Chuck Schumer echoed her sentiments.
The fourth section of the amendment - which has never been invoked - lays out what happens if the president becomes unable to discharge his duties but does not transfer power.
It states that the vice president and the majority of the cabinet would have to declare the president unfit to lead.
Earlier, Donald Trump said there would be an "orderly transition" after Congress certified Joe Biden's win in the presidential election.
"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," the outgoing president said.
The statement was posted on Twitter by Mr Trump's deputy chief of staff, Dan Scavino, after the president was locked out of his social media accounts.
Boris Johnson said it was "completely wrong" for Mr Trump to both "encourage people to storm the Capitol" and cast doubt on the result of last year's presidential election.
The UK prime minister said on Thursday: "All my life America has stood for some very important things - an idea of freedom and an idea of democracy.
"In so far as he [President Trump] encouraged people to storm the Capitol and in so far as the president has consistently cast doubt on the outcome of a free and fair election, I believe that that was completely wrong."
The rioting was preceded by a rally in which Mr Trump told thousands of supporters, including members of far-right groups: "All of us here today do not want to see our election victory stolen by emboldened radical Democrats.
"We will never give up. We will never concede. It will never happen. You don't concede when there's theft involved. Our country has had enough. We will not take it anymore."
While many prominent Republicans are now distancing themselves from Mr Trump, others are still promoting his discredited claims of election fraud.