Twenty-four homemade rockets and a mortar shell were fired into Israel from Gaza on Wednesday, causing shrapnel wounds to three shoppers near a supermarket.
The attacks came as a ceasefire between Israel and Hamas that has existed in name only since early November was set to expire on Friday.
Israel and Hamas, which has ruled the Gaza Strip since seizing power in a bloody coup in 2006, both appear to be deeply conflicted about whether to continue the Egyptian-brokered six-month-old truce and what to do if it ends.
After sending out mixed signals for weeks, Hamas factions in Gaza and in Syria announced two days ago that they would not renew the Egyptian-brokered "hudna" unless it also lifted Israel's blockade of Gaza and was extended to the West Bank.
But at the same time, the Islamic Resistance Movement, to give Hamas its full name, detained members of smaller Palestinian militant factions in Gaza believed responsible for some of the rocket fire.