Four distinct explosions were heard emanating from the base on Monday evening, locals told Sputnik. Plumes of smoke could be seen rising from the facility.
Several drones were launched from the US base immediately after the attack.
The amount of damage to the base or casualties caused by the attacks are unknown, as the US has not yet commented on the incident.
The attack came after an operation in the nearby town of Al-Busayrah earlier on Monday, which was variously reported to have been carried out by American troops or the Syrian Democratic Forces (SDF), a group of US-backed Kurdish militias who formally control the region in the absence of Syrian government authority.
According to reports by Syrian Arab News Agency (SANA), US troops raided the village at dawn, firing indiscriminately into several homes and killing at least four people, the London-based Syrian Observatory for Human Rights said. They also kidnapped several people and took them to an unknown location.
However, the Qatar-based Al Jazeera reported it was SDF forces who carried out the raid.
A similar situation unfolded in September in Al-Shaheel, another village close to the Omar base.
US troops in eastern Syria are not present with the permission of the Syrian government of President Bashar al-Assad in Damascus. They invaded in 2017 under the pretext of fighting Daesh*. Some 900 have remained in eastern Syria after the terrorist group's defeat in support of the autonomous SDF Kurdish militias. The situation has denied the Syrian government the ability to exert control over a considerable part of Syrian territory, in which nearly all of the country's petroleum deposits are located.
*Daesh (ISIL/ISIS/Islamic State/IS) is a terrorist group banned in Russia and many other countries.