In an open letter sent to the Swedish and British representatives of the UN, the signatories said Stockholm and London were setting a "dangerous precedent" by rejecting last month's UN Working group decision, which found that Assange's stay in Ecuador's London embassy was a form of "arbitrary detention."
"We the undersigned, including legal and human rights organizations, academics, and policymakers condemn the reactions of the governments of Sweden and the United Kingdom to the finding by the United Nations Working Group on Arbitrary Detention that Julian Assange is arbitrarily detained," the statement read.
The statement, which includes the signatures of Nobel prize laureate Adolfo Perez-Esquivel, artist Ai Weiwei, Daniel Ellsberg, former US military analyst and source of Pentagon Papers, academic Noam Chomsky and former Greek Finance Minister Yanis Varoufakis, was released as officials meet on Tuesday for the 31 United Nations Human Rights Council meeting in Geneva.
UK, Sweden Setting 'Dangerous Precedent'
The open letter called for the UK and Sweden to respect the UN working group's decision and ensure Assange's right to the freedom of movement.
"The governments of Sweden and the United Kingdom are setting a dangerous precedent that undermines the United Nations Human Rights system as a whole. We urge Sweden and the United Kingdom to respect the binding nature of the human rights covenants on which the decision is based."
The intervention comes after the UK and Sweden rejected the last month's findings, with UK Foreign Minister Philip Hammond dismissing the report as "ridiculous" and "flawed in law."
While Assange's supporters called for him to be granted a free passage to travel to Ecuador, where he has been granted political asylum, British officials said the UN decision had not changed their position on the matter, saying they would arrest Assange and deport him to Sweden should he step foot outside the embassy.
The 44-year-old Australian is still subject to a European arrest warrant over sexual assault allegations allegedly committed in Sweden.
Assange has said he would be happy to answer questions from Swedish prosecutors in London, but has refused to travel to Sweden, amid fears he may be extradited to the US for his role in WikiLeaks releasing thousands of sensitive US military documents.