"Any humanitarian ceasefire that doesn't include the complete withdrawal of its positions in the Gaza Strip, doesn’t enable the residents to go back to their homes and doesn’t allow the evacuation of the wounded, is unacceptable," Sami Abu Zuhri, a Hamas spokesman in Gaza, told Al Jazeera.
An earlier extension of the ceasefire, until midnight local time on Saturday, was broken shortly after 8pm local time, with the Israeli military announcing three mortar rounds had been fired from Gaza into southern Israel.
There was no damage and reports said the military did not regard the incident as a major violation.
Al Jazeera had been told there was no agreement among Palestinian factions in Gaza on extending the ceasefire.
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.
At least 1,150 Palestinians, mostly civilians, have been killed and more than 6,000 injured since Israel launched its offensive on July 8.