More than 160 Gazans have also been injured in the relentless Israeli campaign of air strikes, which continued into Thursday evening with a series of raids near midnight on Beit Hanun in the north of the Strip and in northern Gaza City.
"Three citizens were martyred and 12 injured in an air strike in Beit Hanun," emergency services spokesman Adham Abu Salmiya told.
Eyewitnesses said the strike hit a house, and that two brothers were among the dead.
Earlier Thursday, a 10-month-old girl was declared dead after succumbing to wounds she sustained during an Israeli strike in Gaza City's Zeitun neighbourhood.
Additional strikes throughout the day claimed the lives of a 60-year-old man in Beit Lahiya and a child who died after being wounded in a raid in Khan Yunis.
Since Israel's targeted killing of Hamas military chief Ahmed Jaabari on Wednesday afternoon, Gaza rockets have killed three Israelis and injured 19, three of them soldiers, police and medics said.
Thursday's rocket strike on the southern Israeli town of Kiryat Malachi hit a house, killing two men and a woman, police said.
A spokeswoman said the Israeli military had hit "around 225 targets" in Gaza since it launched its assault with the killing of Hamas military chief Ahmed Jaabari and his bodyguard in an air strike on Gaza City on Wednesday.
Over the same period, 274 rockets fired from Gaza have hit Israel, while 112 have been intercepted by the Iron Dome defence system, the military said.
