Rev 9:
13 Then the sixth angel sounded: And I heard a voice from the four horns of the golden altar which is before God, 14 saying to the sixth angel who had the trumpet, “Release the four angels who are bound at the great river Euphrates.” 15 So the four angels, who had been prepared for the hour and day and month and year, were released to kill a third of mankind.

The river Euphrates runs through Turkey, Syria, Iraq & Iran.