In a new twist between Russia and the US for the ongoing control of the campaign against ISIL in Syria, Russian warplanes bombed U.S. backed Syrian rebels near the Jordanian border on Friday. Pentagon officials say the Russian intervention from two SU-34 Fullbacks caused the U.S. to divert armed aircraft to the scene of the strike.

Moscow backs the Assad dictatorship; the U.S. backs armed rebels who have been trying to overthrow Assad’s regime. The area attacked was a “staging area” camp for counter ISIL forces.

“Russian aircraft conducted a series of airstrikes near al-Tanf against Syrian counter-ISIL forces that included individuals who have received U.S. support. Russian aircraft have not been active in this area of Southern Syria for some time, and there were no Syrian regime or Russian ground forces in the vicinity,” a senior defense official said.

Secretary of Defense Ash Carter was known to be livid about the attack in private, but more reserved in his public statement.