Reports of explosions at Iranian nuclear and missile facilities -- covert attacks, or accidents?

The Washington Post reported on November 12th that an explosion at an Iranian missile base near Tehran killed 17 elite Republican Guards, including a general specializing in long-range missile research. While Iran claimed the explosion was an accident, it comes amidst a string of assassinations, and explosions at other Iranian military bases or energy facilities, that some Iranian officials blame on sabotage orchestrated by "enemies of the Iranian nation," including the U.S. A November 28th Washington Post article published "before and after" photos showing the missile base had been largely destroyed by the blast. 

In a December 3rd article entitled "All eyes on Israel after second Iranian blast," The Australian has reported that smoke clouds billowed above Isfahan, location of an Iranian nuclear facility that converts uranium "yellowcake" into uranium hexafluoride so that it can be enriched. The Iranian regime claims the uranium will be enriched to low levels for use as fuel in atomic reactors, while the U.S. and Israeli governments have alleged the uranium could be enriched to high levels for nuclear weapons manufacture. The article quotes high ranking Israeli officials, who do not deny involvement, and reports that while an Iranian regime spokesman claimed the explosion took place at an unrelated nearby facility, a U.S. official affirmed it was in fact at the nuclear facility.