U.S.-backed forces have taken control of nine villages near the Turkish border in Syria since Tuesday, in an advance toward the Islamic State-controlled town of Manbij.
The U.S. has also carried out airstrikes on Manbij in the last 24 hours which have killed 15 civilians, three of which were children, according to the Syrian Observatory for Human Rights.
Military sources involved in the Manbij operation tell VOA IS militants are evacuating their family members from the town, but are forcing other civilians to remain behind as human shields. Forces say "dozens" of villages outside Manbij have been liberated, with little resistance from IS militants.
The Syrian Democratic forces (SDF), a Kurdish-led alliance working alongside more than 200 American special forces troops, have moved into the jihadist pocket of territory on either side of the Euphrates River, angering Sunni Arab rebels as well as the Turkish, who fear the Kurds are trying to establish their own state along the border.
But the area has long been a target for Washington, which it sees as a key entry point for foreign fighters.
This offensive marks the second of its kind in recent weeks after the SDF last month seized dozens of villages north of Raqqa, the Islamic State's de facto capital in Syria.
Meanwhile, the first humanitarian aid convoy since 2012 entered the besieged Damascus suburb of Daraya on Wednesday. Some aid also flowed into the neighboring suburb of Mouadhimiyeh.
During a May meeting in Vienna, the International Syria Support Group called on the U.N. World Food Program to launch plans for airdrops into besieged areas on June 1, if Syrian President Bashar al-Assad's regime continues to block humanitarian aid deliveries by land.
State Department spokesman John Kirby called Wednesday's deliveries an "important step," but said more needs to be done.
"It is far from sufficient to providing the kind of relief to the hundreds of thousands of Syrian people who are in need," said Kirby, "who need, frankly, sustained and regular access to aid."
He said Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov discussed Syria's aid earlier Wednesday, and the U.S. urged Russia to use its influence with the Assad regime to allow aid convoys through.
He said there was no immediate word on when airdrops might begin.
State Department correspondent Pam Dockins contributed to this report.