Another challenge was protecting the public in light of the "random" targets chosen by attackers.
"[The attacks] were at the equivalent of a place in Meadowbank or Parnell, not places [tourists] were hanging out, necessarily.
"In the first instance you have to work on degrading Isil ... we have to stop, or at least reduce, their capability to reach out to people and build themselves up a following of people who go off and do these kinds of things."
Mr Key said there was a small risk some refugees would be inclined to support Isis but it was unfair to think "because they're Syrian means somehow they're waiting jihadists".
He said the New Zealand security threat was still low but it was constantly being looked at.
Recent events including the attacks in France, as well as attacks on Lebanon and a bomb that brought down a Russian plane, showed the terrorist group was becoming more well-known, Mr Key said.
"They're certainly ramping up their profile and they're sort of trying an outreach of terror, for want of a better term.
"I do think it's part of a very deliberate strategy from these guys," he said.