Several fighters in the Syrian Democratic Forces (SDF) were wounded and required medical care.
Washington and Moscow support separate offensives in the Syrian conflict, with both advancing against Islamic State militants in the eastern region that borders Iraq.
The official added that it appeared that the American citizen surrendered to Kurdish elements of the Syrian Democratic Forces.
The officials, speaking on the condition of anonymity, said the American had surrendered to the Syrian Democratic Forces (SDF), a USA -backed alliance of mostly Arab and Kurdish fighters.
The deal gave safe passage to 600 people, including ISIS fighters and their families, across the Syrian desert from the Lebanese border in southwestern Syria and to the border with Iraq.
The group is supported by United States weapons, air strikes and intelligence as they battle IS in Syria, where the fight is now focused on Raqa and the Euphrates River valley.
"As SDF forces retake territory from ISIS", Manning said, "we have seen cities, towns and communities form civil and military councils and establish that basic governance".
Thousands of foreign fighters from around the globe flocked to Iraq and Syria after Islamic State first captured vast parts of the two countries in 2014 and proclaimed an Islamist caliphate.
But the SDF recently announced its own push toward the city, "Operation Jazeera Storm", and a group of its fighters have made rapid gains, capturing some 300 square kilometers (115 square miles) from ISIS along the Khabur River, which intersects with the Euphrates River just south of the city.
The US military said in a statement that Russian forces struck a target east of the Euphrates River near Deir ez-Zour causing injuries to US-led Coalition partner forces. "We do not allow the regime or its militias to cross to the eastern riverbank". "We put our full efforts into preventing unnecessary escalation among forces that share ISIS as our common enemy", said Funk using an acronym to refer to IS.