Militants picked up where they left off after a 12-hour cease-fire on Saturday, even after Israel offered to extend the period by four hours.
Just two hours after the cease-fire ended, Palestinians resumed firing rockets into Israel from Gaza the armed wing of Islamist group Hamas told Reuters.
Warning sirens wailed across Israel as rockets rained in as far as Tel Aviv.
After the ceasefire began early on Saturday, Gazans took advantage of the lull in fighting to retrieve their dead and stock up on food, flooding into the streets to discover scenes of massive destruction in some areas.
Israel's security cabinet met in the evening to discuss international efforts, led by U.S, Secretary of State John Kerry, to secure a longer lasting truce, but at least one minister said the military operation should be expanded.
The Associated Press reported:
Hamas said it fired five rockets at Israel late Saturday after rejecting Israel's offer to extend a 12-hour humanitarian cease-fire by four hours, casting new doubt on international efforts to broker an end to 19 days of fighting.
Hamas said two of the rockets were aimed at Tel Aviv. Police in Israel's second-largest city dispersed a peace rally attended by several thousand people because of the threat, a spokesman said.