The Prime Minister says he is seriously concerned about New Zealanders joining the terrorist group Islamic State.

John Key told Newstalk ZB's Leighton Smith the Government was aware of a small group of Kiwis who may pose a threat.

READ MORE: FBI: We've identified 'Jihadi John'

"They are brutal, they are highly sophisticated, they're well organised and they're spreading out.

Advertisement

"We are not immune, so we know there are foreign fighters fighting overseas and we know and can identify at least a reasonably sized that group that want to leave and join that cause," he said.

Mr Key has said in the past that the Government had concerns about New Zealanders returning home after fighting with foreign rebel groups as they could be a terrorist threat.