Foreign Minister Julie Bishop has warned that destroying the marauding Islamic State group entirely will be "impossible" and that it may become a long-term threat similar to al-Qaeda.

Reflecting the immense difficulties facing the West as it wrestles with how to stop the militant group creating terror in the Middle East, Ms Bishop said the Islamic State (also known as ISIL) is an ideology as well as a military force and will therefore survive efforts to stamp it out.

She was speaking after the United States sought to quell lingering uncertainties about its goals and strategy for Iraq and Syria by announcing at a Nato summit the establishment of a 10-country "core coalition" – including Australia – to tackle the Islamic State.

Asked whether that coalition's goal was to destroy the group, Ms Bishop told Fairfax Media on Sunday: "I think that's impossible … Have we destroyed al-Qaeda?"