Here is a summary of reactions from officials, activists and celebrities to the 47-year-old Australian's arrest.
UK: Assange is 'no hero'
"Assange's arrest shows "in the United Kingdom, no one is above the law," British Prime Minister Theresa May declared.
British Foreign Minister Jeremy Hunt said Mr Assange "is no hero," stating: "He has hidden from the truth for years and years and it is right that his future should be decided in the British judicial system."
UK Labour leader defends Assange
UK Labor party leader Jeremy Corbyn issued a statement in defence of the WikiLeaks founder, saying free speech should be protected. He has also urged the UK government to oppose any move to extradite Mr Assange to the United States.
Ecuador: 'sovereign right'
"Ecuador has decided with sovereign rights to withdraw the diplomatic asylum to Julian Assange for repeatedly violating international conventions and the protocol of cohabitation," President Lenin Moreno said on Twitter.
Moreno's government said Ecuadoran nationality granted to Assange in 2017 was also withdrawn "due to various irregularities found in his paperwork."
WikiLeaks: asylum halt 'illegal'
"Ecuador has illegally terminated Assange's political asylum in violation of international law," WikiLeaks said on Twitter.
Australia: 'due process'
Australian Foreign Minister Marise Payne said she was "confident" that Mr Assange "will receive due process in the legal proceedings he faces in the United Kingdom." She said consular officers would visit Assange in detention.
UN expert: rights 'violations'
Ecuador has exposed Mr Assange "to a real risk of serious violations of his human rights" by placing him closer to extradition to the US, the United Nations special rapporteur on summary or arbitrary executions, Agnes Callamard, told AFP by email.
Snowden: 'Dark moment'
"Assange's critics may cheer, but this is a dark moment for press freedom," US whistleblower Edward Snowden said on Twitter.
Russia: UK 'strangling freedom'
"The hand of 'democracy' is strangling freedom," Russian foreign ministry spokeswoman Maria Zakharova said on Facebook.
Ecuador leader branded 'traitor'
"The greatest traitor in Ecuadorian and Latin American history, Lenin Moreno, allowed British police to enter our embassy in London to arrest Assange... What he has done is a crime that humanity will never forget," Ecuador's former leader Rafael Correa wrote on Twitter.
Sweden accuser: reopen case
"We will do everything we can to get the prosecutors to reopen the Swedish investigation so that Assange can be extradited to Sweden and be prosecuted for rape," his accuser's lawyer Elisabeth Massi Fritz told AFP.
'Pamela Anderson: 'shock'
"I am in shock. How could you Equador (sic)? (Because he exposed you). How could you UK?" wrote the former "Baywatch" actress Pamela Anderson, reportedly a close friend of Mr Assange, on Twitter.
In colourful language, she suggested Britain acted under pressure from the United States and to divert attention from its woes over Brexit.