US President Donald Trump predicted Wednesday that IS will have lost all of its territory by next week.
Earlier on Saturday, the Syriac Military Council, which fights under the SDF umbrella, announced they had sent an assault group for the "final operation/attack to defeat ISIS in Baghouz".
SDF spokesman Mustafa Bali told AFP, "The battle has started".
The SDF, spearheaded by the Kurdish YPG militia, has driven ISIS out of a swathe of territory in northern and eastern Syria over the last four years. US, French, British and other forces are also actively looking for wanted ISIS operatives among those fleeing the combat zone with civilians.
But a top USA general said on Tuesday the group would pose an enduring threat following the US withdrawal, as it retained leaders, fighters, facilitators and resources that would fuel a menacing insurgency.
The fighting was concentrated near al-Omar field, Syria's largest. While the bounty doesn't explicitly reveal the reason why the veteran foreign terrorist fighter has fallen in disfavour, intelligence officials, cited by The Guardian, suggest that he led the unsuccessful coup attempt aimed against the leader, Sputnk says.More news: Amid uproar, Vatican clarifies Pope's comments on 'sexual slavery' of nuns
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But a series of separate military operations, including by the SDF, have left its proto-state in tatters.
The coalition has been training and providing air support to the Syrian Democratic Forces, which launched an offensive on the last pocket of jihadist territory in September 2018.
"The territorial caliphate, which has not yet been wiped out, is being defeated", minister Florence Parly said in Baghdad.
USA officials have said in recent weeks that IS has lost 99.5 per cent of its territory and is holding on to fewer than 5 square kilometres in Syria in the villages of the Middle Euphrates River Valley, where the bulk of the fighters are concentrated.
The Britain-based Syrian Observatory for Human Rights, a war monitor, said SDF fighters are advancing "cautiously" due to mines planted by IS gunmen. But activists and residents say Isis still has sleeper cells in Syria and Iraq, and is laying the groundwork for an insurgency.
It said 401 civilians, including 144 children and teenagers, have been killed since then.