A senior defence chief in Australia says that country's air strikes against Islamic State militants in Iraq are putting the terrorist group under immense pressure.

Since the international mission to disrupt and degrade IS began in October, Australian super hornets have contributed more than 180 sorties.

During ground operations, Australian Special Forces are training local Iraqi soldiers in counter-terrorist tactics, co-ordinating air-strikes and managing dozens of improvised explosive devices.

Chief of Joint Operations Vice Admiral David Johnston says IS is coming under immense pressure and the militants' momentum has been checked.