Iran is off targets when it comes to united states, israel is not allowed to strike iran without permission. Blaming hezbollah is much easier, gives israel the green light to restart hostiilities against its northern adversary with little or no fallout. With Syria falling to pieces, Hezbollah would have more difficulties, one may suspect that u.s, israel may use this bombing as a casus belli to attack lebanon. Resembles the Eilat attacks where egyptian militants attacked an israeli troop convoy, and Israel retaliated by attacking Hamas instead of egypt. Once again egypt was off limits, but casus belli was used to restart hostilities with Hamas.
Historic flooding in U.S.'s Carolinas kills 13 (DPA)
from the article: Pentagon: Terror attack in Bulgaria bears hallmarks of Hezbollah