More than 100 fires have killed one man and destroyed more than 200 homes in New South Wales state since Thursday.
Fire investigators found that a massive fire near the city of Lithgow, west of Sydney, began October 16 at a nearby Defence Department training area, and that the blaze "was started as a result of live ordnance exercises" at the army range, the Rural Fire Service said in a statement.
The fire has burned 47,000 hectares (180 square miles) and destroyed several houses, but no injuries or deaths have been reported in the blaze. It was downgraded from the highest emergency category today.
The Defence Department was also investigating any link between the exercise and the fire.