Nation's skies crowded with multiple air forces

Further discussions expected between United States, Russia as the risk of unintended conflict grows amid growing involvement

The skies over Syria are increasingly crowded - and increasingly dangerous. The air forces of multiple countries are on the attack, often at cross purposes in Syria's civil war, sometimes without coordination. And now, it seems, they are at risk of unintended conflict.

The latest entry in the air war is Russia. The Russians, who are not coordinating with the Americans, reportedly also have hit at least one US-supported rebel group.