7 photos: Tense moments between Obama and Putin  Barack Obama and Russian President Valdimir Putin toast during a luncheon hosted by United Nations Secretary-General Ban Ki-moon during the 70th annual U.N. General Assembly on September 28 in New York City.  7 photos: Tense moments between Obama and Putin  Obama and Putin shake hands while posing for a photo ahead of their meeting at U.N. headquarters on September 28 in New York.  7 photos: Tense moments between Obama and Putin  Putin speaks with Obama during the Asia-Pacific Economic Cooperation summit in Beijing, China on November 11, 2014. U.S.-Russia relations have descended to a new low since Russia annexed Crimea in March.  7 photos: Tense moments between Obama and Putin  Obama and Putin share a comical and awkward moment on a large split-screen during an international ceremony on the stretch code-named Sword Beach, in Ouistreham, France, to commemorate the Allied invasion of Normandy on June 6, 2014. Obama and Putin had an informal 15-minute chat during lunch at the ceremony that marked the 70th anniversary of the D-day landings. "It's a positive thing that they spoke, but more needs to be done," a senior U.S. official said at the time.  7 photos: Tense moments between Obama and Putin  Putin greets Obama at the G-20 summit on September 5, 2013 in St. Petersburg, Russia. The United States and Russia have been squaring off over the bloody civil war in Syria.  7 photos: Tense moments between Obama and Putin  Obama listens to Putin after their bilateral meeting in Los Cabos, Mexico on June 18, 2012 on the sidelines of the G-20 summit. The meeting was the first time Obama and Putin held face-to-face talks since Putin returned to the president's office earlier that year. Obama said he and Putin discussed the conflict in Syria and "agreed that we need to see a cessation of the violence, that a political process has to be created to prevent civil war."  7 photos: Tense moments between Obama and Putin  Obama, who had become U.S. President six months earlier, enjoys tea with then-Prime Minister Vladimir Putin and members of the American delegation at Putin's dacha on July 7, 2009 in Moscow.
Two Russian and two U.S. aircraft came within visual range of each other -- separated by just 10 to 20 miles -- over Syria Saturday.