The 39-year-old, who is living at a friend's mansion in eastern England, must wear an electronic ankle tag and observe a curfew as he appeals against his extradition to Sweden to face rape and sexual assault allegations.
In a statement released to some media including The Daily Telegraph newspaper, WikiLeaks bemoaned Assange's position.
"He has not been charged with a crime in any country. The conditions of his detention are excessive and dehumanising," the organisation said.
"Whilst fighting this battle, and trying to continue with his important work for freedom of information, he is being forced to remain in unfair and undignified conditions."
Assange maintains that the claims against him by two women he met during a seminar in Sweden last August are politically motivated because of his work.
The Australian former computer hacker rocked the diplomatic world and infuriated Washington last year when his website began releasing hundreds of thousands of secret US State Department and military documents.
WikiLeaks began publishing around 250,000 cables in which US diplomats give their often candid views on world leaders, to Washington's acute embarrassment.
He was detained in London under the European arrest system in December.
Assange has claimed his greatest fear is eventual extradition to the United States, where his lawyers argued he could be sent to the Guantanamo Bay detention facility or face the death penalty.
"The allegations as they are made do not amount to crimes in the UK. If he were to go to Sweden he would be kept in detention indefinitely and incommunicado," WikiLeaks said in the statement.
"If charged, he will be subjected to a trial held in secret. He will not be allowed to see all the evidence against him.
"Outside observers will not be able to scrutinise the merits of the case."
"The Swedish government has refused to state that it will not hand over Mr Assange to the United States. This is why he is fighting this disproportionate and unfair extradition order."
His appeal hearing at the High Court in London will take place on July 12-13.