A strike on a house in the southern city of Rafah killed two men, emergency services spokesman Ashraf al-Qudra told AFP, and a separate raid killed a young man who witnesses said was an Islamic Jihad militant.
Another Rafah strike shortly afterwards left one man dead, Qudra said, while a raid on the home of Mohammed al-Arjani in the southern city of Khan Yunis killed his son Abdullah, 19.
Some of the first raids on today morning targeted homes of senior Hamas officials, including Mahmud al-Zahar, but there were no reports of casualties in those strikes.
It was the ninth day of Israel's Operation Protective Edge, which aims to stamp out rocket fire from Gaza militants.
Since July 8, militants have fired nearly 1,000 rockets and mortars into the Jewish state, and Israel has carried out around 1,500 strikes against targets inside the Gaza Strip, according to the army.
Yesterday saw Israel's first fatality, when a man died from a rocket attack near the Erez border crossing.
Four Israelis have been seriously injured by rocket fire, and Israel's air strikes have wounded more than 1,500 Palestinians.
The Gaza-based Palestinian Centre for Human Rights said on Sunday, when the Gaza toll stood at over 150, that three quarters of the dead were civilians.
And on Monday, a senior UN official said more than a quarter were children.
International efforts towards a ceasefire collapsed yesterday, as Hamas rejected an Egypt-proposed truce, and Israel resumed its bombing raids several hours later after continued rocket fire.