Australia's military chiefs expect Islamic State to be defeated in Syria within days or weeks.
The extremist group has collapsed down to the south-eastern part of Syria and its fighters only hold about 700 square metres of land.
Acting Chief of the Defence Force David Johnston believes a defeat of the group's self-declared caliphate is imminent.
"The judgment that we are seeing is that within days or weeks that remaining small pocket of quite hardcore fighters in that area are likely to be defeated by the SDF forces on the ground," he told a Senate committee on Wednesday.
"So the land-based caliphate element of Daesh is likely to be defeated within the next few weeks."
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Donald Trump has announced the United States will withdraw its troops from Syria by April.
Australian military chiefs, who have been in discussion with counterparts in the US, expect the withdrawal to be completed within six months.
The potential knock-on impacts for Australian and other allied troops in neighbouring Iraq have been communicated to Pentagon chiefs.
Vice Admiral David Johnston was asked for his view on whether the imminent ISIS defeat meant a US presence in Syria was no longer needed.
"In the next few weeks it should not require it because the land-based caliphate should be defeated," he said.
