"We had an agreement with the Russians that they would not move in the south. There was a de-escalation zone that the Russians had agreed to. They now have clearly violated that," Pompeo told Sky News Arabia.
Pompeo said the United States and Russia were not in agreement with regard to the activities in southern Syria, but pointed out that Washington is engaging all concerned parties there, including Russia and Iran, "to honor the commitments they have made in the various political processes that have been undertaken with respect to Syria."
Syria has been in a state of war since 2011 with opposition groups and terrorist organizations fighting the Syrian Arab Army to topple the government of President Bashar Assad.
In July 2017, Russia, Jordan and the United States agreed on establishing de-escalation zones in Syria's southern provinces Daraa, Quneitra and Suwayda.
There are currently four agreed de-escalation zones in Syria. The first zone is in Idlib and parts of neighboring Latakia, Hama, and Aleppo provinces; the second in the north of the central Homs province; the third in Eastern Ghouta near Damascus; and the fourth in certain parts of the southern Daraa and Quneitra provinces.