Julian Assange has said he will not consider leaving the Ecuadorean embassy in London unless the US government drops its "immoral" investigation into WikiLeaks.

Assange has been sheltering in the embassy since June as part of his attempt to avoid extradition to Sweden to face rape allegations. He fears he will ultimately be sent to the United States to face interrogation over the whistleblowing website, which he founded.

In a CNN interview in the embassy, Assange said the standoff could end if the US government drops its investigation. "It's an immoral investigation," he said. "It breaches the first amendment, it breaches all the principles that the US government says it stands for and it absolutely breaches the principles the founding fathers stood for and which most of the US people believe in."

Assange broke his bail conditions in June when he took refuge in the embassy in Knightsbridge after he lost a supreme court challenge to the validity of the European arrest warrant that demanded his return to Sweden for questioning. He was due to be sent within days when he took up residence in the diplomatic mission having been granted political asylum.

His lawyers and the Ecuadorean government contend that travelling to Sweden could lead to his extradition to the US, where he could face charges over WikiLeaks' publication of thousands of US diplomatic cables.

US soldier Bradley Manning is two years into his military solitary confinement for allegedly leaking hundreds of thousands of US state secrets, many of which ended up on the WikiLeaks website. He is currently awaiting trial and could be sentenced to life in prison if found guilty.

"There's an attempt to extradite me without charge and without evidence, allegedly for the purpose of questioning," said Assange. "Meanwhile, the FBI has been engaged in building this tremendous case, now up to 41,235 pages."

In the interview, Assange compared life in the embassy to "living on a space station". "There's no natural light," he said. "You have got to make all your own stuff. You can't go out to the shops. But I've been in solitary confinement. I know what life is like for prisoners – [this is] a lot better than it is for prisoners."

His interview came after WikiLeaks released more than 100 US defence department files on Thursday disclosing the military's detention policies in Guantanamo Bay and Iraq, dating from the September 11 attacks until 2004.

Assange said the documents showed that "policies of unaccountability" had allowed prisoners to be abused with impunity. The destruction of video interviews or the failure to record them, as revealed in the files, had led to a situation "where abuse can occur and it can't be discovered".