The truce is due to begin at 08:00 local time. Efforts to negotiate a seven-day ceasefire are still ongoing.
Earlier US Secretary of State John Kerry said he was still confident of a longer ceasefire, despite media reports that Israel had rejected one proposal.
More than 800 Palestinians, mostly civilians, and 38 Israelis have died since the conflict started on July 8.
A spokesman for Hamas, the Islamist group that controls Gaza, Sami Abu Zuhri said there was “national consensus on a humanitarian truce… for 12 hours on Saturday”.
The Israel Defense Forces (IDF) later confirmed the truce on Twitter, but said it would “continue to locate and neutralize terror tunnels”.
“We will respond if terrorists choose to exploit this time to attack IDF personnel or fire at Israeli civilians,” it said in a statement.
The news came shortly after Israeli Defense Minister Moshe Yaalon warned that ground operations in Gaza could soon be broadened “significantly”.
Moshe Yaalon told soldiers: “You need to be ready for the possibility that very soon we will instruct the military to significantly broaden the ground operation in Gaza.”
Hamas has previously said it would not agree to any long-term truce that did not lead to an end to Israel’s blockade of the Gaza Strip.
According to the UN, Israeli air strikes killed a further 68 people in Gaza on Friday, bringing the total number of Palestinian dead to about 870.
There were also clashes during protests in the West Bank which left at least five Palestinians dead.
Palestinians in the West Bank had been taking part in a “Day of Rage” against Israel’s military operation in the Gaza Strip.
Meanwhile Israel’s military said its Iron Dome defense system had intercepted several rockets fired across the border by Hamas.
Later it said that two of its soldiers had been killed in Gaza during the night.
Israel launched its military offensive on July 8 with the declared objective of stopping Hamas firing rockets into Israel.
It has since extended its operation to destroy tunnels dug by militants to infiltrate Israel.
Several foreign ministers, including John Kerry, are due to hold a meeting in France on Saturday to seek a diplomatic solution.
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