The base, which is located in the Badiyeh al-Sha'afa area, will be equipped with "advanced military tools and systems," according to the sources.
The reports come a week after Sharfan Darwish, spokesman for the Manbij Military Council of the US-backed Syrian Democratic Forces (SDF), said that the US military had created a new military base in the Syrian region of Manbij about three months ago, following Ankara's threats to seize control of the area.
Darwish was quoted by Reuters as saying that "after the Turkish attack on Afrin and the increase in Turkish threats towards Manbij, coalition forces built the base to monitor and protect the border [between the combatants]."
For its part, Fars reported last month that a new US military base had been established at the al-Omar oilfield in southeastern Deir ez-Zor, where a variety of military hardware, including missile systems and armored vehicles, had been deployed.
On March 28, Turkey warned that it would push its military operation in the northern district of Afrin further to Manbij, if the US-backed Kurdish People's Protection Units (YPG) forces decline to pull out of the region.
Ankara is seeking to gain control of Manbij as part of its Operation Olive Branch, which was launched on January 20, 2018. Ankara has blacklisted the YPG, the backbone of the SDF, as an affiliate of the Kurdistan Workers' Party (PKK), which is outlawed in Turkey as a terrorist organization.
In a separate development in April, US Secretary of Defense James Mattis declared that the US military would not withdraw its forces from Syria, but would expand operations there and "bring in more regional support."
The US-led coalition has been launching airstrikes against what it calls Daesh* targets in Syria since 2014, in a mission that was approved neither by Damascus nor the UN. Right now, about 2,000 US troops are deployed in Syria.
*Daesh (ISIL/ISIS/Islamic State), a terrorist group banned in Russia and a spate of other countries