The United States and Russia reached a “memorandum of understanding” Tuesday about how both its air craft can safely fly over Syria’s skies without running into each other and when necessary communicate with their rival pilots, the Pentagon announced Tuesday.Pentagon spokesman Peter Cook suggested the agreement did not designate what both sides considered a safe distance between its aircraft. He could not say what happen if Russia violates the terms of agreement, but rather that a climate of mistrust continues, despite the memorandum.

Cook added that the agreement applied to all members of the U.S.-led coalition conducting air strikes against the self-proclaimed Islamic State and that the agreement applied to both manned and unmanned aircraft. And it created a channel for communication between the two rivals over Syrians skies.Since Russia launched its air war on ISIS, there have been a handful of close encounters between the Russian and U.S. flights, including an instance in which they came within several hundred feet on each other. The U.S. generally considers at least 20 miles a safe distance.

U.S. officials believe Russia flew near its some of its aircraft to get a better view of the U.S. technology, particularly its drones. Indeed, Russia has posted videos of its aircraft coming dangerously close to its American counterparts.

-- Nancy Youssef