Fiji’s top immigration official has confirmed categorically that Islamic State fighter Neil Prakash is not a Fijian national, meaning the Morrison government’s stripping of Prakash’s Australian citizenship is not lawful.

Speaking for the first time to Australian media, Fiji’s director of immigration, Nemani Vuniwaqa, also said no one from the Fijian government was consulted before Australia declared Prakash had lost his Australian citizenship, despite the fact a second citizenship was vital to the legal process in Australia.

Asked whether he was absolutely certain Prakash was not Fijian, he said: “Yes I am. He is not a Fiji citizen.”

A leading Fiji-based lawyer has also examined the case and concluded of Prakash that “it is almost certain that he is not a Fiji citizen now”.

Mr Vuniwaqa threw the case into question last week when he told a local paper Prakash was not Fijian, dramatically undermining Home Affairs Minister Peter Dutton’s announcement in late December that Prakash had been stripped of his Australian citizenship.