At least three mortars were fired from Gaza toward southern Israel on Thursday morning, some two hours after a temporary lull in hostilities went into effect to allow humanitarian supplies into the area.
The mortars fell in open areas and no injuries were immediately reported, the Israeli military said. Mortars are smaller and have a more limited range than rockets.
Israel, which said it would honor the cease-fire but not sit idle if attacked, did not immediately respond.
The five-hour long temporary halt in fighting went into effect at 3 a.m. ET, requested by the United Nations to offer a brief respite in a conflict that has killed more than 220 people.
Banks opened for the first time in 10 days in Gaza and residents poured into the streets.
Red Cross officials visited hospitals and damaged houses to assess medical needs, and worked with local officials to quickly fix water pipelines, which has left hundreds of thousands without water.
There were no reported air strikes since the cease-fire began. Still, the fear of death hung heavily over Gaza. The health ministry warned civilians to avoid gathering in squares.
"Should the humanitarian window be exploited by Hamas or other terror organizations for the purpose of launching attacks against Israeli civilian or military targets the IDF will respond firmly and decisively," the Israeli military said.
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