Australian fighter jets attacking Islamic State in the Middle East might soon run out of targets to strike.
The US-led coalition fighting IS no longer considers the group a combat threat, despite fears militants are plotting "spectacular attacks" in the Iraqi and Syrian deserts.
"They no longer have an army that we saw present itself in 2014," spokesman Colonel Ryan Dillon told reporters during a briefing this week.
The 3000 or so IS militants left in Iraq and Syria were moving into uninhabited areas and returning to insurgent-like tactics, he said.
The number of strikes carried out by the coalition has rapidly dwindled during the past three months from 1500 in September, to 700 in October and 200 in November.
Belgium is bringing its six F-16 Falcons fighter jets home at the end of December after an 18-month stint flying sorties in the Middle East.
Four hundred US Marines are headed home and won't be replaced.
Australia has six Super Hornets conducting missions across Iraq and Syria, along with an air-to-air refuelling tanker and Wedgetail early warning and control aircraft.
Defence Minister Marise Payne said the government regularly reviews Australia's contribution to the effort to combat IS.
"In line with all decisions of this nature, the government would consult with Iraq and coalition partners," she told AAP.