Update. A few more postings with links from LGF (one, two, three). Inconclusive at this point. (Note: LGF is right-wing, comments are often childish and explosive while the author's postings are not; on the contrary.)
Update. Now BBC says it's not Israeli fault. But it does not, really; simply quotes sources (like Israeli minister of defense) and puts their words in the title. BBC more often tends to go against Israel than for it, but in either case building titles this way is irresponsible.
Update. Same shit: Jerusalem Post quotes Human Right Watch in the title ("Report: IDF caused Gaza beach blast") and quotes head of the IDF investigation in the body ("Israel had an airtight case and was definitely not behind the explosion").
Update. Krauthammer's musings.
Update. Now, according to Jerusalem Post, Human Rights Watch is correcting itself: it was not artillery fire, but perhaps unexploded ordnance (they say "ordinance", it's a difficult word, all right). Some comments from a blogger follow.
Update. Seems not to be 155 mm shells. Quote: "we would never do that! Heaven forbid we accuse them of such base activities. That would be racist."