In all, 18 Gazans have been killed and more than 65 wounded since Israel unleashed the strikes following a Hamas attack on an Israeli school bus Thursday. An anti-tank rocket struck the bus, seriously wounding a 16-year-old boy and injuring the driver.
After Israel's devastating military offensive in the winter of 2008-2009, Gaza's Hamas rulers had largely observed a cease-fire, and it was not immediately clear why the Islamic militants chose to end their relative restraint. Israel, in turn, has pledged to strike back hard for the bus attack, in an attempt to restore the deterrence created by the Gaza war.
Early Saturday, an Israeli airstrike struck a car near Rafah in southern Gaza, killing three Hamas militants. Hamas said one of its top commanders, 29-year-old Tayser Abu Snima, and two of his assistants were killed.
Later, Hamas said a tank shell killed another militant near the Jabalya neighborhood in Gaza. The Israeli military said it was not aware of a strike involving a tank shell.
Overall, the Palestinian death toll since Thursday includes 11 militants, a Hamas policeman and six civilians.
Hamas and Islamic Jihad fired more than 15 missiles into Israel Saturday. The rockets reached the vicinity of the Israeli cities of Ashdod, Ashkelon and Beersheba. The military confirmed that its newly deployed Iron Dome defense system knocked some of them down. No Israelis were wounded in the attacks.
Reinforced rooms and early warning systems also have helped keep Israeli casualties low.
The interception of missiles in recent days mark a defense coup for Israel. Iron Dome is the first system worldwide to knock down missiles at such altitude and trajectory.
Israel has said it would hit back hard for the bus attack.
Israeli Prime Minister Benjamin Netanyahu said Friday that the attack on the school bus "crossed a line" and warned that "whoever tries to harm and murder children will pay with their life."
Most of the schoolchildren on the bus had gotten off shortly before the attack. Had the attack caused a significant death toll, the Israeli response would surely have been more severe, perhaps even leading to another major Israeli offensive.
Hamas spokesman Sami Abu Zuhri said Saturday that the group's attacks were still "limited and controlled" but that continued Israeli strikes may force it to escalate in response. He said that Israel was trying to break the control of Hamas in Gaza.
"The occupation government is responsible for this escalation," he told reporters in Gaza. "We want to make a clear point that we shall not allow them to achieve their goals and they must know that they will fail to force the Palestinians to give up."
Hamas has said the bus attack was in retaliation for the killing of three fighters in an airstrike earlier in the week.
It is not clear whether Hamas was trying to provoke a new conflagration with that attack, if it was not fully in control of all of its fighters, or if it believes Israel would pull back before invading Gaza again. Israel was condemned internationally after the Gaza war.
Thousands of rockets from Gaza have hit Israeli towns and cities since 2001. Israel's attempts to stop the rockets have included military incursions and covert operations abroad aimed at disrupting Hamas' efforts to procure arms.