The officials in Gaza said Israel attacked security targets in Gaza City and also in northern and southern parts of the crowded coastal territory.
The violence threatened to unravel an already shaky three-day-old Egyptian-brokered truce called on fighting that erupted on Monday after a raid across Egypt's Sinai border into Israel in which an Israeli man and two of the gunmen were killed.
Israel responded to that attack, blamed on pro al-Qaeda Salafist militants, with punishing air raids in Islamist-ruled Gaza, which also borders on Egypt.
Ten Palestinians, many of them militants but also a 14-year-old boy, have been killed in these raids.
Two militants died in separate air raids on Gaza on Friday, which the Israeli military said was in response to rocket fire .
Hamas militants had conditionally pledged to adhere to a truce brokered by Egypt on Wednesday, if Israel also withheld fire. Israel never formally commented on the deal but its officials have vowed to respond to any rocket fire from Gaza.
Israel said Gaza militants had also fired more than 130 rockets at Israel since Monday, causing no casualties, but disrupting life in an area where a million Israelis live and where civilians have been urged to remain near shelters.