Israeli military officials said Hamas fired three mortar shells from Gaza hours after a humanitarian cease-fire went into effect Thursday.
Rockets were launched into southern Israel at noon local time, causing no injuries, Israeli police spokesman Micky Rosenfeld said.
There was no immediate reaction from Hamas, whose armed wing Qassam Brigades has been behind many of the rocket attacks toward Israel.
Israel and Hamas had begun observing a five-hour humanitarian cease-fire, as fighting extended into a 10th day.
The two sides agreed to the pause following a request by the United Nations so that supplies could be delivered to Gaza. Despite the call to lay down arms, Israeli military personnel told Al Jazeera that the probability of a ground offensive in Gaza is "increasing."
Israel has activated 40,000 troops and currently has approval for another 8,000, said the military official, who spoke on condition of anonymity.
In 2012, during the last Israeli campaign in Gaza, the military called up 70,000 troops but did not invade.
Fighting continued in the lead-up to the start of the cease-fire Thursday at 10 a.m local time. Police in the southern Gaza town of Rafah said tank shells landed on a house, killing at least three civilians.
The Israeli military said 15 rockets were fired into Israel Thursday morning. It also said it prevented an attack by 13 fighters who infiltrated into Israel through a tunnel from Gaza.
The cross-border fighting has so far killed more than 220 Palestinians and one Israeli, according to officials.
Robert Serry, the U.N. special coordinator for the Middle East peace process, had asked Israel to agree to the "unilateral humanitarian pause" so that supplies can be delivered to Gaza, U.N. deputy spokesman Farhan Haq told The Associated Press. Serry will "urge the parties in Gaza to respect that pause," Haq said.
The humanitarian pause came after Israel intensified airstrikes overnight on Wednesday, as it promised to ramp up its offensive and ordered some 100,000 Palestinians to evacuate their homes ahead of more strikes.
Four Palestinian children were killed on a Gaza beach and one critically wounded when Israel's naval gunboats shelled the area Wednesday, according to journalists and medics at the scene.
"The kids were playing football on the beach. They were all ... under the age of 15," Ahmed Abu Hassera, 22, told Reuters.
"When the first shell hit the land, they ran but another shell hit them all ... It looked as if the shells were chasing them," Hassera, whose shirt was stained with blood, said.
Ashraf al-Qidra, spokesman for the Gaza Health Ministry called it a "cowardly crime."
A Palestinian man carries the body of a boy, whom medics said was killed by a shell fired by an Israeli naval gunboat, on a beach in Gaza City, July 16, 2014.Mohammed Talatene/Reuters
Earlier Wednesday, the Israeli army dropped leaflets and issued prerecorded phone calls to residents of northeast Gaza, telling them to evacuate.
“For your own safety, you must evacuate your homes now and at once go toward central Gaza. You have until 8 a.m. on Wednesday … It is forbidden that you go back to the areas cited above until further notice,” the warning said.
Hamas called the orders “psychological warfare” and urged residents to stay in their homes, the Palestinian news website Maan News reported. On Sunday, Israel warned residents of Beit Lahiya in northern Gaza to leave, causing at least 17,000 civilians to seek shelter in United Nations installations.
Human Rights Watch said in a statement Wednesday that "providing warnings does not make an otherwise unlawful attack lawful," and condemned both Israeli and Gazan attacks on civilians. Israeli airstrikes investigated by HRW revealed the targeting of civilian structures, often resulting in the unlawful killing of civilians. "Deliberate or reckless attacks violating the laws of war are war crimes," the rights group said in a statement.