Talking Points Memo now has up this AP story from which I quote:
Spain says it and other European countries were told that fugitive NSA leaker Edward Snowden was aboard the Bolivian presidential plane that was diverted to Austria this week, causing a diplomatic row.
Foreign Minister Jose Manuel Garcia-Margallo said Friday on Spanish National Television “they told us that the information was clear, that he was inside.”
It is hard to believe that the "they" can be other than sources within the US Government.