Among the dead were 10 members of one family in Beit Lahiya, including a former prisoner, Abdel-Fattah Abu Mahadi, who had been released as part of the ceasefire, along with his wife, children and grandchild.
Other strikes killed seven people in Gaza City and 10 more in Khan Younis, including several young children.
Israel has carried out daily bombardments since ending a ceasefire with Hamas last month, cutting off Gaza’s 2 million residents from food and medicine.
There was no immediate comment from the Israeli military. Officials say they target militants, while Palestinians say nowhere in Gaza is safe.