'Israeli fire' kills four in Gaza

The house targeted in the blast, in the Shajaiyeh district, belonged to a known Hamas activist, locals quoted by the Associated Press news agency said.

At least three people are said to have been hurt in the explosion.

Israel launched its military offensive in the Gaza Strip three weeks ago after a soldier was captured by militants linked to Hamas's military wing.

Cpl Gilad Shalit was captured in a cross-border raid near the Gaza Strip.

The Israeli military has not confirmed its involvement in the latest incident.

Hamas sources said the blast had killed a militant from their group, as well as his mother and two of her grandchildren.

The house which was destroyed is near the Karni crossing point where Israeli troops and tanks have been massed for the past three weeks.

Israeli bulldozers are reported to be in the area as the search for tunnels and weapons continues.

They said Israeli helicopters had also attacked the area.

The blast in Shajaiyeh came hours after Israeli forces ended a two-day assault on the Maghazi refugee camp in central Gaza in which they killed at least 14 Palestinian militants and civilians.