Home Affairs Minister Peter Dutton insists the revocation of terrorist Neil Prakash’s Australian citizenship is legally sound because he is also a Fijian national but has refused to detail the supporting advice from the government’s lawyers.

The stripping of Prakash’s citizenship was thrown into doubt on Tuesday after a senior Fijian immigration official said the Islamic State member was not a national of Fiji.

Australian terrorists can have their citizenship revoked under a 2015 law but only if they have a second citizenship and therefore would not be rendered stateless.

“The legal advice available to the government based on all the intricate detail and fact of this particular matter is that Mr Prakash is by operation of law a citizen of Fiji,” Mr Dutton said.