The Syrian government had not given the United States permission to deploy any troops in the country, according to the deputy minister.
“Of course, they were not,” Deputy Foreign Minister Gennady Gatilov told reporters, when asked whether the US troops had been deployed in Syria legally.
In October, the United Sates deployed 50 US troops in Syria to help local militia to fight against the Daesh jihadist group.
Earlier this week, US President Barack Obama said that he would send an extra 250 special operations forces to Syria in the coming weeks to support local militia in the anti-Daesh fight.
Vast territories in Syria and neighboring Iraq have been occupied by Daesh, which has proclaimed a caliphate on the land under its control. The notorious militant group is banned in Russia, the United States and many other countries.