Aust link to Iraq casualties investigated

An investigation is underway to determine if there was any Australian involvement in an air strike that caused civilian casualties in Iraq.

Defence force chief Mark Binskin said no Australian aircraft were involved in the March incident.

"We're working with our partners to assess the extent to which Australian personnel were involved in the coalition approval process," the air chief marshal told a Senate estimates hearing in Canberra.

Defence Minister Marise Payne said 55 per cent of Islamic State territory in Iraq and Syria had been taken and held so far and an estimated 1.5 million displaced people had been able to return home.

Western Mosul is close to being liberated.

The fight against IS would then move on to smaller towns in Iraq such as Tal Afar, Hawijah and along the Euphrates River Valley; and to Syria.

"We expect efforts to isolate and ultimately liberate Raqqah will be particularly tough, given the symbolic significance of Raqqah as the self-described capital of its caliphate," Senator Payne said.