Two more Gazans died in Israeli air strikes on Thursday, raising the toll to 15, as militants fired 250 rockets over the border, killing three Israelis, officials said.
Aside the from the deaths, around 150 Gazans have been injured in 22 hours of Israeli air strikes, medics said.
Hamas health ministry spokesman Ashraf al-Qudra said a strike in the northern town of Beit Lahiya had killed a 60-year-old man.
And the emergency services said a child had died of wounds he sustained in a strike on Khan Yunis earlier on Thursday.
Since Israel's targeted killing of a top Hamas chief on Wednesday afternoon, Gaza rockets have killed three Israelis and injured another 16, police and medics said.
Soon after dawn on Thursday, an Israeli air strike east of the southern Gaza Strip town of Khan Yunis killed three Palestinians, medical officials said.
The armed wing of Hamas, the Ezzedine al-Qassam Brigades, said that the three men were all members and were hit as they travelled in a motorcycle-taxi.
Later in the day an air strike hit northern Gaza where two people were killed and another person was injured, medics said.
It was not immediately clear if they were civilians or militants.
Thursday's rocket strike in Kiryat Malachi "killed ... two males and a female in two apartments in a building which was hit," police spokesman Micky Rosenfeld told AFP.
Since the violence erupted when Israel killed a top Hamas militant on Wednesday afternoon, the military has hit "around 225 targets" in Gaza, a spokeswoman said.
In the same period, "at least 138 rockets" hit Israel, while another 81 were intercepted by the Iron Dome anti-missile system, she said.
The bloodshed began at around 1400 GMT on Wednesday when Israel killed Hamas military chief Ahmed Jaabari and his bodyguard, sparking a fierce bout of cross border fighting which continued into the night.
Six more people died during various strikes later on Wednesday, including two children, officials from the Hamas-run health ministry said as Gaza hospitals went on high alert.