Reported in multiple news outlets and dsicussed on various blogs...

Here is the 14 June article from the Australian - Hamas 'Mined Gaza Beach'.

An Israeli army investigation into the explosion on a Gaza beach last Friday that killed seven members of a Palestinian family has concluded it was almost certainly caused by a Palestinian mine, not an Israeli shell, according to the Israeli media yesterday.

The military wing of Hamas had seized on the deaths to declare an end to its ceasefire with Israel, and a resumption of large-scale hostilities between Palestinian militants and Israel seemed possible.

However, it was unclear whether the Israeli findings on the beach blast would be credible to the Palestinians.

Israel, which expressed regret for the deaths, was initially inclined to accept an artillery shell was responsible, because Israeli warships fired six shells in the area. The impact of five was observed hundreds of metres from the beach, but the sixth shell was unaccounted for.

However, suspicions of a possible other cause were aroused when it was learned Hamas operatives had scoured the area and taken away pieces of shrapnel. Shrapnel was also removed from the bodies of the wounded brought to Israeli hospitals.

Israel's Channel Two television said shrapnel was found in a wounded child brought to Israel, and it was not the metal used in artillery shells.

The Haaretz daily reported that photographs of the crater on the beach suggested it was caused by an explosion from below, not a hit from above...