The latest gain comes as Turkey's Prime Minister Binali Yildirim says the US gave assurances that weapons used by fighters it supports against Daesh in Syria will not be a threat to Turkey.
US-backed Syrian militias said they seized a major dam on the Euphrates river from Daesh on Sunday, their latest gain as they push towards Raqqa city.
The Syrian Democratic Forces – a major part of which Turkey accuses of links with local terror group PKK – said they captured Baath Dam in the morning, renaming it Freedom Dam. The hydroelectric dam lies some 22 kilometres upstream of Raqqa, Daesh's base of operations in Syria.
Addressing reporters in Turkey's capital, Ankara, late on Saturday, Turkish Prime Minister Binali Yildirim said the US informed Turkey before the operation started.
Yildirim reiterated Turkey's disapproval to the US allowing SDF to conduct the Raqqa operation. He said that the US made assurances that the weapons used by the SDF in Syria will not be a threat to Turkey.
"They [the US] told us that it was not an option but an obligation [to cooperate with SDF in Raqqa] and that the tactical cooperation with them would not be maintained for long after the [Raqqa] operation," Yildirim said.
The difference between Washington and Ankara on Syria mainly derives from how they regard the armed groups in the region.
Turkey views the YPG which makes up a majority of the SDF as the Syrian extension of the PKK, a group that has waged a three-decade insurgency against the Turkish state and is considered a terrorist organisation by Ankara and the European Union.
With the help of the US-led coalition's air strikes and special forces, the SDF has been encircling Raqqa in a bid to retake the city which Daesh has used as a hub to plan attacks abroad.
A spokesman for the YPG, Nouri Mahmoud, said, "The dam has been completely liberated." Mahmoud said the fighters were combing nearby villages for mines and shoring up their defence lines.
The advance means the SDF now hold all three major dams along the Euphrates, after gaining control of Syria's largest dam last month. The alliance advanced in recent months to within several kilometres (miles) of the centre of Raqqa, facing fierce resistance from Daesh.
Fighting since late last year has displaced tens of thousands of people according to United Nations sources, with many flooding camps in the area.