The Government is still working through exactly how it would deal with jihadists returning to New Zealand from overseas conflicts, Attorney-General Chris Finlayson says.
Prime Minister John Key on Wednesday said five New Zealand citizens or residents are fighting alongside Islamic State in Syria.
Mr Finlayson said New Zealand is acting in accordance with a United Nations resolution passed on 24 September.
"One of the things it does is to look at developing and implementing prosecution, rehabilitation and reintegration strategies for returning foreign terrorist fighters.
"So I would think there are probably two classes of such fighters, one would be those who got over and thought, gee this isn't what we bargained on, we need to get out of here and get back to New Zealand - and that's fine we're here to help such people.
"And then secondly the ones who come back to promote jihad on these shores and then the issue really is, does the Crimes Act or Terrorism Suppression Act cover this sort of thing, if not, is there a gap and it will need to be filled."
An important principle is that governments cannot arbitrarily detain or imprison people, without a substantive, criminal offence having been committed, he said.
Mr Finlayson said the Government had to tread carefully and would not be rushing any legislative change that may be required.
The Government also intends to pass laws making it easier for the Security Intelligence Service to carry out surveillance, and allow passports to be cancelled for longer, as soon as possible.
Up to 40 people are being monitored by the government because of their involvement with or support for IS.
Security consultant Dr Paul Buchanan told Morning Report the Government must be careful about correctly identifying the people leaving New Zealand to fight with Islamic State.
"For example there are members of the Syrian community who for family and personal reasons have chosen to go back and may well be fighting for the Free Syrian Army which of course is backed by the West in the fight against (Syrian President) Assad."