I guess it's the latter. Now the investigation needs to get going. Iran won't hand over the black box to the Boeing/US.A plane engine catches fire, something causes the motor to come apart, all of those turbine blades go somewhere...between an engine tearing itself apart and a general explosion? Could be anything unless some trigger happy Iranian gunner got spooked.
Source: Canada PM says he won't rest until he gets answers about downed jet
From the article -- a case of journalists trying to stir shit up.
Trudeau was pressed by journalists about whether the United States should be held at least partially responsible for the tragedy, given that tensions in the region ignited after a U.S. drone attack killed a top Iranian general.