The United States is accusing Russia of bombing U.S.-supported anti-Islamic State forces in southern Syria near al-Tanf.

A senior Pentagon official told the Washington Examiner that a series of airstrikes were conducted by Russian planes in an area of southern Syria, where Russian aircraft have "not been active for some time."

"Russia's latest actions raise serious concern about Russian intentions," the official said on condition of anonymity. "We will seek an explanation from Russia on why it took this action and assurances this will not happen again.‎"

The official said the airstrikes targeted "Syrian counter-ISIL forces that included individuals who have received U.S. support."