Anonymous U.S. officials are quoted by the NY Times stating explicitly that a Hezbollah suicide bomber attacked the Israeli tourist bus yesterday. While this is entirely possible, I think we should remember the bizarre bombing plot of a few months ago in which a small-time Iranian drug dealer was alleged by the Justice Department to have direct links to the Revolutionary Guards, and to have plotted the assassination of the Saudi ambassador. By the way, this is the same person, Bandar ibn Sultan, just appointed chief of Saudi intelligence.
We haven't heard a peep from the government about the so-called Saudi bomb plot though Obama had it all over the front pages at the time, since it was a useful cudgel to use against Iran. So I think caution is warranted in approaching this latest claim.