The shell came from an Israeli tank
Three Palestinians including a 12-year-old boy have been killed in an Israeli army search for militants in the West Bank town of Hebron.
Forces surrounded a building early on Tuesday.
Two bodies which have yet to be identified were later discovered in the building.
During the raid the forces fired tank shells. Shrapnel from one shell killed the 12-year-old, who was in a nearby building.
The Haaretz newspaper identified him as Thaer Sayuri.
Israel has stepped up attacks on militant leaders since a Hamas suicide bomber blew up a Jerusalem bus on 19 August, killing 22 people.
The Israeli Prime Minister, Ariel Sharon, has said his forces will hunt and kill all the leaders of Hamas.
At least 11 Hamas militants and four civilian bystanders have been killed in missile strikes in Gaza since the Jerusalem bus bombing.