The storming of the US Capitol on Wednesday by supporters of President Donald Trump drew a wave of condemnation from around the world, as international leaders threw their support behind efforts in Washington to return order to the city.
British Prime Minister Boris Johnson called for an end to the "disgraceful scenes" in Washington.
"The United States stands for democracy around the world and it is now vital that there should be a peaceful and orderly transfer of power," Mr Johnson said on Twitter.
Prime Minister of Canada, Justin Trudeau, shared a message of sorrow and optimism.
"Canadians are deeply disturbed and saddened by the attack on democracy in the United States, our closest ally and neighbour," Mr Trudeau said.
"Violence will never succeed in overruling the will of the people. Democracy in the US must be upheld, and it will be."
French President Emmanuel Macron said in a video message on Twitter, "What happened today in Washington, DC, is definitely not American. We believe in the power of our democracies. We believe in the strength of American democracy."
Prime Minister of New Zealand Jacinda Ardern shared the sentiments of many Americans by expressing on Twitter that what took place on Wednesday was "wrong" and that "Democracy - the right of people to exercise a vote, have their voice heard and then have that decision upheld peacefully should never be undone by a mob."
Indian Prime Minister Narendra Modi said in a tweet, Distressed to see news about rioting and violence in Washington DC. Orderly and peaceful transfer of power must continue. The democratic process cannot be allowed to be subverted through unlawful protests."
Earlier about 1,100 National Guard members were sent to support law enforcement in the US capital to counter a pro-Trump mob attempting to thwart a peaceful transfer of power.
One woman died after being shot in the violence and a curfew was introduced across the city.
Pentagon spokesman Jonathan Hoffman said defence leaders had been in contact with the city and congressional leadership.
President-elect Joe Biden called the violent protests on the US Capitol “an assault on the most sacred of American undertakings: the doing of the people’s business".
He demanded that President Donald Trump immediately make a televised address calling on supporters to cease the violence and “unprecedented assault".
Mr Trump later issued a restrained call for peace but did not ask his supporters to disperse. He later tweeted a call for “no violence”.
Later still, he released a video asking for protesters to go home and for peace, but still repeated claims of voter fraud.
Nato Secretary General Jens Stoltenberg said developments in Washington were "shocking".
Mr Stoltenberg called for the "respecting of this democratic election", in a rare intervention by Nato in US politics.
The President of the EU Commission, Ursula von der Leyen said: “I believe in the strength of US institutions and democracy. Peaceful transition of power is at the core.
"Joe Biden won the election. I look forward to working with him as the next President of the US."
German Foreign Minister Heiko Maas on Wednesday called on supporters of Mr Trump to "stop trampling on democracy".
"Trump and his supporters should finally accept the decision of American voters," Mr Maas tweeted.
"The enemies of democracy will be pleased to see these incredible images from Washington DC. Inflammatory words turn into violent actions."
German Finance Minister Olaf Scholz, who is also Vice Chancellor, condemned the "disturbing images" from Washington.
"This is an unbearable attack on democracy," he tweeted, adding that Mr Trump had "deeply divided the country".
Mr Biden, who beat Mr Trump in November's election, "has a tough job ahead to bring Americans back together again", Mr Scholz wrote.
Greek Prime Minister Kyriakos Mitsotakis wrote on Twitter: “Extremely troubled by the violence and horrible events taking place in Washington DC.
"American democracy is resilient, deeply rooted and will overcome this crisis.”
Italians watched the events with shock, having always considered the US to be the model of democracy and the country that rescued them after their country's fascist descent in the Second World War.
“This is the widely anticipated outcome of Trump-ism,” tweeted a retired Italian centre-left politician, Pierluigi Castagnetti.
“And unfortunately, it won’t end today. When politics is replaced by deception and fanaticism of the people, the drift is inevitable.”
European Parliament President David Sassoli, who leads one of the largest legislatures in the world, also denounced the scenes at the Capitol.
The EU has spent four difficult years dealing with the Trump administration, and its top officials have repeatedly said they are looking forward to a better relationship with Mr Biden.
“This is insurrection. Nothing less. In Washington,” tweeted Carl Bildt, a former prime minister of Sweden.