The head of the SDF media office, Mustafa Bali, told Reuters that the main battle will be launched on the evening of February 9 and its mission will be to eliminate the last remnants of "the terrorist organization".
The SDF arrested 63 suspected militants in ISIS's former Syrian capital Raqa on Thursday during an operation against sleeper cells, it said in a statement.
Bali said there could be up to 600 IS fighters still inside the pocket, a lot of them foreigners.
While ISIS will soon no longer have fixed positions anywhere in Iraq or Syria, its surviving fighters have reverted to guerrilla warfare and remain a potent force.
Bali said in the last 10 days SDF fighters had handled the battle "patiently" as civilians were evacuated from the besieged villages.
At the height of its rule, IS controlled territory the size of Britain.More news: Measles cases confirmed in northwest Harris County
More news: Philadelphia 76ers Trade Markelle Fultz To Orlando Magic
More news: Saudi crown prince had threatened to use 'bullet' on Khashoggi - NY Times
"There is of course a safe corridor and civilians are coming out daily, and this reduces their number in Baghouz until we can be sure the town is free of civilians".
"It should be formally announced sometime, probably next week, that we will have 100 percent of the caliphate", Mr Trump told representatives of a 79-member, US-led coalition fighting ISIS.
The U.S. -led coalition has said it is not discussing the timeline of the U.S. withdrawal from Syria.
The country's Kurds have largely stayed out of the conflict, instead developing semi-autonomous institutions in parts of the country's northeast under their control.
The Kurdish People's Protection Units (YPG) and their female equivalent, the Women's Protection Units (YPJ), have formed the backbone of the SDF.
"Currently, ISIS is regenerating key functions and capabilities more quickly in Iraq than in Syria, but absent sustained [counterterrorism] pressure, ISIS could likely resurge in Syria within six to twelve months and regain limited territory", the report added, quoting officials with the U.S. Central Command. "We have chosen a political agreement with Damascus because we don't want secession from Syria", senior Kurdish official Badran Jia Kurdi told AFP.