A spokesman for the US-backed Democratic Forces of Syria said his forces would resume the attack on Bagouz, the last pocket of a terrorist in eastern Syria, if no more civilians or fighters were to leave by Saturday afternoon.
Syria's demilitarized forces have slowed their offensive on the enclave in Baguoz near the Iraqi border to allow several thousand to leave over the past few weeks.
A month ago, Syria's democratic forces began what it described as the "final battle" for the return of the Baguoz, and those who left were described as terrible conditions fraught with dangers and tribulations.
Syria's Democratic forces said a week ago that it believed all civilians had already left and resumed the offensive, sparking a new wave of displacement, some of them followers of Da'ash, their families and hundreds of surrendering fighters.
Mustafa Bali, director of the Media Center of the Syrian Democratic Forces, said the enclave did not witness any exits on Friday.
"They are waiting until Saturday morning or Saturday to allow any civilians who are still on the way out. If no one comes out, the troops will resume the attack."
A senior US defense official in Washington said the process of regaining control of the Baguz could take days or even weeks. The official, who spoke on condition of anonymity, said about 20,000 people and their families had left Baguoz so far.
"We have consistently erred as our partners in the Syrian Democratic Forces have done in terms of estimating the numbers of fighters who leave and whom we consider to be in contact with women and children," he said.
The official added that Syria's democratic forces are holding about 4,000 suspected militants from Iraq and Syria and more than 1,000 foreign fighters .