That fear proved well-grounded. While it probably doesn't seem as big of a deal now — in this era when we just serially assassinate heads of state we don't like without any pretense otherwise — the US indeed did direct its European allies to intercept the plane of Bolivian president Evo Morales, based on the (incorrect, as it turned out) suspicion that Snowden was on board.

https://en.wikipedia.org/wiki/Evo_Morales_grounding_incident