A statement from the Israeli military said it would hold fire on Thursday, from 10:00 to 15:00, to allow residents to stock up on supplies.
Palestinian officials say Israeli raids have killed 220 Gazans and wounded almost 1,800 since July 8.
Hamas militants have fired more than 1,200 rockets, killing one Israeli.
The ceasefire had been requested by the UN and other international organizations.
But the statement by the Israeli Defense Forces (IDF) added that Israel would respond “firmly and decisively” should the humanitarian window be used by militants “for the purpose of launching attacks against Israeli civilian or military targets”.
The move was announced hours after Hamas, the dominant force in Gaza, confirmed that it had rejected an earlier ceasefire proposed by Egypt.
Israel initially observed the ceasefire on Tuesday, but resumed its strikes amid continued rocket fire from Gaza.
Four children were among those killed in Israeli strikes on Wednesday. They died while playing on a beach near Gaza City.
The IDF said they were “carefully investigating” the incident, adding that “based on preliminary results, the target of this strike was Hamas terrorist operatives”.
“The reported civilian causalities from this strike are a tragic outcome,” the statement said.
Israel launched its Operation Protective Edge on July 8. Its stated objective is to halt Palestinian rocket attacks on Israel, but the UN says most of those killed in Gaza have been civilians.
Gaza militants fired dozens of rockets into Israel on Wednesday.
Senior Hamas official Sami Abu Zuhri told reporters that the group did not accept Egypt’s ceasefire proposal and that Israel would pay a heavy price for its strikes.
Hamas – designated a terrorist organization by Israel and the US, among others – is demanding the easing of border closures in Gaza and the release of Hamas prisoners.
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