Shelling by Israeli forces has killed nine Palestinians, including three civilians in Gaza.
A Hamas missile hit at an Israeli school bus on Thursday, seriously wounding a teenager.
The BBC reports Israel has since launched more than 20 raids on the Gaza Strip, killing 13 people. About 45 others have been wounded.
Police said at least 15 rockets had been fired into Israel since dawn on Friday.
Israel says it holds Hamas responsible for all attacks coming out of the territory, even if it is other groups carrying them out.