An Iranian asylum seeker is 44 days into a hunger strike as the Immigration Department tries to force him to return voluntarily to Iran or stay in detention indefinitely, which his lawyers describe as being trapped in a "Kafkaesque nightmare".

The 33-year-old man, who cannot be named for legal reasons, is in Wickham Point Immigration Detention Centre in Darwin in a near-critical condition after refusing to eat since November 1, losing 23 kilograms.

The Wickham Point Immigration Detention Centre 50 kilometres outside Darwin. Credit:Glenn Campbell

Speaking through an intermediary, the man told Fairfax Media that staff from the Immigration Department are constantly pressuring him to voluntarily return to Iran. Iran refuses to accept the forcible return of its nationals from Australia.

"[The Immigration Department] always give me negative news and they are constantly saying to me, you have to go back, you have go to back," he said.