Fiji has thrown further doubt on the Federal Government's declaration that terrorist Neil Prakash has lost his Australian citizenship.

Key points: Neil Prakash was born in Melbourne to a Fijian father

Neil Prakash was born in Melbourne to a Fijian father The Federal Government insists "clear" advice shows he is Fijian

The Federal Government insists "clear" advice shows he is Fijian Fiji's Prime Minister says Prakash "cannot come here"

Home Affairs Minister Peter Dutton announced on Saturday that the former Islamic State recruiter was the 12th dual national to lose Australian citizenship for engaging in terrorism.

Those who only hold Australian citizenship cannot lose it, as that would leave them stateless.

Prakash was born in Melbourne to a Fijian father and Cambodian mother.

Fiji's Prime Minister Frank Bainimarama on Thursday told a local newspaper Prakash "cannot come here because he does not qualify".

"At any rate, he is a terrorist and a member of ISIS," he told the Fiji Sun.

"We don't entertain them, nor do we accommodate them."

Mr Bainimarama's comments have fuelled the diplomatic standoff between Canberra and Suva.

But the Federal Government insists its Citizenship Loss Board carefully considered the case and received "clear" advice stating Prakash is a Fijian citizen.

"That board deemed that he had a citizenship— [was] entitled to a citizenship of another country," Treasurer Josh Frydenberg said on Thursday.

"Australia will remove the citizenship of these dual nationals who are engaged in terrorist activities."

Ministers have said Fiji was informed of the determination before it was publicly announced.

But the Government has not said whether Fiji was consulted before senior public servants concluded Prakash was a dual national and therefore able to lose his Australian citizenship.

Labor demands advice about Prakash's Fijian citizenship

The head of Fiji's Immigration Department, Nemani Vuniwaqa, earlier this week told the Fiji Sun Prakash was not Fijian and had never applied for citizenship.

"Neil Prakash has not been or is [not] a Fijian citizen," Mr Vuniwaqa said.

"For a child of a Fiji citizen born overseas, the parent has to apply for citizenship for the child to become a Fiji citizen."

The Federal Opposition has demanded the legal advice about Prakash's Fijian citizenship be released.

"Peter Dutton's refusing to release that advice," Labor's Jason Clare said.

"It all looks like another Peter Dutton stuff up."

Prakash could appeal to the High Court.

He is currently in jail in Turkey, where he faces multiple charges related to being a member of the Islamic State group.