Last Updated Jul 26, 2014 1:45 AM EDT
JERUSALEM -- A 12-hour humanitarian cease-fire has begun to allow civilians in Gaza to receive aid and evacuate to safer areas.
The Israeli military says Saturday's 12-hour pause began at 8 a.m. (1:00 a.m. EST, 0500 GMT). It warned the military "shall respond if terrorists choose to exploit" the lull to attack Israeli troops or civilians. The military said "operational activities to locate and neutralize tunnels in the Gaza Strip will continue."
Previous humanitarian cease-fires have been cut short by fighting.
Civilians on both sides have been hardest hit over the past 18 days. Nearly 900 Palestinians and 40 Israelis have been killed.
The lull was agreed upon by both sides after U.S. Secretary of State John Kerry failed to broker a weeklong truce as a first step toward a broader deal.
The Israeli military said in a statement the lull would start at 8 a.m. local time Saturday and end at 8 p.m. local time. The statement warns that the military "shall respond if terrorists choose to exploit" the lull to attack Israeli troops "or fire at Israeli civilians." It also says that "operational activities to locate and neutralize tunnels in the Gaza Strip will continue."
The ceasefire was negotiated by U.S. Secretary of State John Kerry, who said this before leaving Cairo Friday night: "The whole world is watching a tragic moment after tragic moment unfold and wondering when is everybody going to come to their senses?"
The possible advance towards peace came late Friday, after Kerry earlier admitted that he had not yet reached a deal between Israel and Hamas to call a seven-day humanitarian truce in the Gaza war.
Kerry's comments at a Friday evening press conference in Cairo closing days of shuttling between the Egyptian capital, Jerusalem and the West Bank trying to work out a week-long pause in fighting that has killed more than 820 Palestinians and 38 people in Israel.
Speaking alongside the U.N. secretary-general and the Egyptian foreign minister, Kerry insisted that there was a general agreement on the "concept" of a truce but that both sides had concerns over details of carrying it out. He said he was "confident" that the truce's fundamental framework would succeed.
In a statement issued shortly after Kerry spoke, Israel's defense minister announced Israel may soon broaden its ground operation in the Gaza Strip significantly. In a statement by Defense Minister Moshe Yaalon office, he is quoted as telling troops in the field that "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 is paying a very heavy price and will pay an even heavier price," Yaalon said. "At the end of the operation, Hamas will have to think very hard if it is worth it to taunt us in the future."
Gaza fighting continued alongside the truce efforts. Israeli airstrikes hit more than 80 sites in Gaza, while militants in the tiny Mediterranean strip fired 50 rockets at Israel, the army said. Among the sites hit in Gaza were 30 homes, including that of a leader of the Islamic Jihad group who was killed along with his sons, Palestinian officials said.
And unrest sparked by the conflict intensified in the West Bank, where five Palestinians were killed during protests against the Israeli operation in Gaza.
Thursday's deadly attack on a UN school in Gaza provoked outrage over night. At least 15 civilians trying to avoid the violence were killed.
CBS News' Barry Petersen spoke with a Palestinian man who lost a small daughter and whose teenage son was gravely wounded.
"It's like I've lost part of myself," said Abed Rabu at his 18-month-old daughter's graveside. "She used to smile and play -- and then suddenly she was gone."