"We consider the fact that, despite the preliminary arrangements, the United States did invite [the Revolutionary Commando Army], which is translated as Partisans of Revolution, for the protection of convoys inside the so-called exclusive zone completely unacceptable," Zakharova said.
READ MORE: US Deploys 600 Additional Troops in Syria's At-Tanf — Reports
She added that Moscow also had questions regarding Washington's refusal to let the representatives of the Syrian Arab Red Crescent charity in the Rukban refugee camp located near al-Tanf.
"This means that they have something to hide," she indicated.
The US military currently occupies a 34-mile zone around its base in al-Tanf, where it has been training Syrian opposition forces since 2016.
The base has become the subject of criticism as Damascus and Moscow have expressed concerns that Washington was "spewing Daesh* mobile groups who make inroads to launch subversive terrorist operations against Syrian troops and civilians."
*Daesh (also known as ISIS/ISIL/IS) is a terrorist group banned in Russia
