According to Al-Watan newspaper, the base in the town of Ash Shaddadi was shelled by unknown militants.
Within the past several months, the illegal US military bases in the provinces of Al-Hasakah and Deir ez-Zor have been repeatedly attacked by unknown militant groups. One such attack left two US citizens missing.
The US troops, jointly with the Kurdish-led Syrian Democratic Forces, are keeping control over a part of northeastern Syria. The US military is concentrated around oil and gas fields in Al-Hasakah and Deir ez-Zor.
The Syrian government sees the US presence on its soil as a violation of national sovereignty and an attempt to seize its natural resources.