Haaretz reported the Palestinian militants had fired about 120 rockets and mortars into Israel since Thursday night. Israeli authorities reported there were no casualties, though homes and farm buildings were damaged.
Tens of thousands of people sought safety in bomb shelters.
The Israeli military said its Iron Dome missile defense system had intercepted eight rockets fired at Ashkelon and Be'er Sheve since Thursday, Haaretz said.
The Palestinians said Saturday that in addition to those killed, more than 60 people had been injured by the Israeli artillery, tank and air attacks on the Gaza Strip. Adham Abu-Salmiya, head of emergency medical services in Gaza, said most of the casualties were civilians and that the dead included several women and children.
Israeli military said it regretted the deaths of civilians but said Hamas has been conducting its operations from within civilian populations.
Haaretz said Hamas denounced the absence of international condemnation of the Israeli attacks.
The Israeli newspaper said the Arab League was to convene an emergency meeting Sunday in response to a demand by Palestinian Prime Minister Mahmoud Abbas. Abbas called on the Arab League and the European Union to pressure Israel to stop the fighting.
Hamas military wing spokesman Abu Obeida said the militant group would respond to Israeli aggression.
"Palestinian blood is not for forfeiting," he said.
The recent round of violence stems from a Hamas missile attack against an Israeli school bus that critically injured a 16-year-old boy.
Israeli Prime Minister Binyamin Netanyahu said Friday the attack on the civilian bus "crossed the line" and that "whoever tries to hurt and murder children will have no immunity."
"When Palestinian civilians are killed in these kinds of strikes, the population should only complain to Hamas, which continues to turn its own citizens into a protective vest," an Israeli military official said.
The mounting Gaza death toll is the largest number of Palestinian casualties since the 2008-2009 Israeli military offensive that left more than 1,000 Palestinians dead.