Five members of a Palestinian family and a passerby have been killed by Israeli tank fire in the Gaza Strip. As Robert Berger reports from VOA's Jerusalem Bureau, the incident could torpedo efforts for a ceasefire.

An Israeli tank shell slammed into a Palestinian home in Gaza, killing four children, under six years old, and their mother. The family was eating breakfast when the explosion occurred.

The Israeli army said it used tanks and aircraft to target Palestinian gunmen in an area often used to fire rockets. A tank shell apparently went astray and struck the home.

The Islamic militant group Hamas, which rules Gaza, promises revenge.

Hamas spokesman Fawzi Barhoum is calling on all factions to launch attacks against Israel. The response came quickly, as militants in Gaza fired rockets across the border.

Israeli Defense Minister Ehud Barak blames Hamas for the incident, saying the army is operating in Gaza because of daily Palestinian rocket attacks on Israeli border communities.

Barak says Israel will continue to strike at Hamas. He accuses the group of using civilians as human shields.

The incident occurred several days after Israel rejected an Egyptian-mediated ceasefire offer from Hamas. Israel says Hamas would use a truce to rearm for the next round of violence. And, now, Hamas says Israel will be responsible for the escalation resulting from what it describes as the "massacre" in Gaza.