U.S. Army General Joseph Votel, head of the U.S. Central Command, cautioned that the exact timing would depend on the situation in Syria, where U.S. -backed fighters have launched a final assault against Islamic State enclaves near the Iraqi border.
Across the border in Syria, US special forces remain to "advise and assist" the SDF, and are involved in screening people fleeing from the fighting.
"We have special units whose job it is to direct civilians to corridors they can cross" to safety, he said.
More than 23,000 Syrian civilians and foreign nationals fled eastern Syria this past week as the SDF, which includes Kurdish YPG militia fighters, prepared to move on IS in Deir el-Zour governorate, according to local officials and activists.
Kurdish-led forces in eastern Syria prepared Friday for a push on the last remaining speck of the Islamic State group's "caliphate" where diehard jihadists and their families are holed up.
That would herald an end to the almost five-year-old war aimed at pushing the Islamic State out of its self proclaimed "caliphate", the once vast stretch of territory spanning Syria and Iraq that at its peak was roughly the size to Britain.
The assault began on Saturday after nearly 20,000 people were evacuated from the ISIS-held area in the eastern province of Deir el-Zour along the Iraqi border, according to SDF spokesman Mustafa Bali.
It's estimated that between 500 and 1,000 civilians are inside, Bali said.
In the northeastern Kurdish-majority city of Qamishli on Saturday, SDF fighters stood to attention at the funeral of a YPJ fighter who died fighting IS.
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Near her coffin, a mourner held up a doll dressed in a bridal gown, part of tradition for young women fighters who die before they are married.
The group, however, retains a presence in Syria's vast Badia desert, and has claimed a series of deadly attacks by sleeper cells in SDF-held areas.
The Observatory said 12 IS gunmen attacked the SDF and clashed with them for several hours until most of the attackers were killed early Saturday.
The Kurds, who have de facto semi-autonomy in north-eastern Syria, are also engaged in behind-the-scenes diplomatic talks over the fate of the region.
The president's sudden decision surprised many in his own administration as well as coalition allies such as Turkey and an alliance of Kurdish and Arab militias that fought Islamic State with USA military support.
Mr Trump said last December that he had ordered a complete troop withdrawal from Syria, a shock announcement that left the Kurds scrambling for new allies.
The regime has made a military comeback with Russian military support since 2015, and now holds nearly two-thirds of Syria.
SDF-held areas make up a third of the whole country, and Damascus has repeatedly said it would eventually see them revert to government control.