Russia and the United States tentatively agreed Tuesday to resume talks on how to prevent conflicts between their warplanes in the skies over Syria, even as concerns mounted about the potential for a broader confrontation in the Middle East between the two powers. After days of complaints from U.S. and NATO officials about a lack of cooperation and risky maneuvers by Russian warplanes, Russia’s Defense Ministry offered to hold another round of discussions with the Pentagon on avoiding a midair disaster or a hostile encounter among their fighter jets, drones and other aircraft over Syria.