Julian Assange's British legal team has requested Australian diplomatic help as fears grow for his health and mental state in a London prison.

The WikiLeaks founder has been held in HM Prison Belmarsh since his April 11 arrest at the Ecuadorian embassy, where he had lived in asylum for almost seven years.

Julian Assange's supporters are increasingly concerned about his health and mental state in a British prison. Credit:Getty

Australian officials told a Senate estimates hearing on Thursday that diplomats had not heard back from Assange's lawyer since writing to her last week asking that she raise with him their offer of consular assistance.

The 48-year-old is fighting US attempts to extradite him to face 17 counts of spying and one of computer hacking in relation to WikiLeaks' release of thousands of classified Pentagon files regarding the Iraq and Afghanistan wars.