Christensen,who hasrepeatedly endorsed claims of voter fraud on social media,was last year slapped with a warning from Facebook for misleading claims about"dodgy votes"boosting President-elect Joe Biden.
British Prime Minister Boris Johnson said the scenes in Washington were"disgraceful".
"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,"he said on Twitter.
Other allies were similarly appalled at what they described as an attack on American democracy,though some said they believed US democratic institutions would withstand the turmoil. Some leaders singled out Trump for harsh criticism.
"Trump and his supporters should finally accept the decision of the American voters and stop trampling on democracy,"German Foreign Minister Heiko Maas wrote on Twitter."From inflammatory words come violent deeds."He added"contempt for democratic institutions has disastrous effects".
Fiji's Prime Minister Frank Bainimarama,who first seized power of the Pacific Island nation in a bloodless military coup in 2006,the country's third coup in six years,before winning two democratic elections,called the protesters actions"an affront to democracies around the globe".
"True and genuine democracy is a precious treasure that no nation should ever take for granted. We are confident the USA will soon close this ugly chapter once and for all,"he tweeted.
In Nigeria,which has seen several coups since independence — including one led decades ago by President Muhammadu Buhari,who most recently entered the office via a vote,one of the President's personal assistantsBashir Ahmad tweeted:"The beauty of democracy?"with a shrug emoji.
Chilean President Sebastián Piñera and Colombian President Iván Duque were among those in Latin America who denounced the protesters,but both also said they were confident American democracy and the rule of law would prevail.
Brazilian Supreme Court justice and the head of the country's electoral court,Luis Roberto Barroso tweeted:"In this sad episode in the US,supporters of fascism showed their real face:anti-democratic and aggressive". He said he hoped"American society and institutions react with vigour to this threat to democracy".
Venezuela,which is under US sanctions,said the events in Washington show the US"is suffering what it has generated in other countries with its politics of aggression".
Venezuelan President Nicolás Maduro has survived US-backed opposition efforts to oust him despite accusations of human rights abuses,civil unrest and a humanitarian crisis that has forced millions to flee the oil-rich country.
In Puerto Rico,many people took to social media and joked that the US territory no longer wanted statehood. Independence,they said,looked appealing for the first time in decades.
In fact,it was that pursuit of independence that marked one of the last times the U.S. Congress was stormed violently. Four members of Puerto Rico's Nationalist Party opened fire on the House floor in March 1954,wounding five lawmakers.
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European Parliament President David Sassoli,who leads one of the largest legislatures in the world,also denounced the scenes at the Capitol. The European Union has spent four cantankerous years dealing with the Trump administration,and its top officials have repeatedly said they are looking forward to a better relationship under the Biden administration.
Carl Bildt,a former prime minister of Sweden tweeted:"This is insurrection. Nothing less. In Washington".
Canadian Prime Minister Justin Trudeau said his country was"deeply disturbed"by the events in the US,Canada's closest ally and neighbour.
"Violence will never succeed in overruling the will of the people. Democracy in the US must be upheld — and it will be,"Trudeau tweeted.
Volkan Bozkir,president of the 193-member United Nations General Assembly,said he was saddened by the developments. But,he tweeted,"I believe that peace&respect for democratic processes will prevail in our host country at this critical time."
With AP
Trump Biden 2020
Understand the election result and its aftermath with expert analysis from US correspondent Matthew Knott. Sign up toThe Sydney MorningHerald's newsletterhere,The Age'shere,Brisbane Times'here andWAtoday'shere.