Israeli warplanes struck targets across Gaza, killing a child on Friday in retaliation to rocket fire after a 72-hour truce expired without a breakthrough on a longer-term ceasefire.
Palestinian militants started the rocket salvos ahead of the truce expiry at 0500 GMT, and Gazans again fled homes in fear before Israeli Prime Minister Benjamin Netanyahu warned of a forceful response.
The bloodshed ended a three-day lull that had followed a month of fighting between Israel and Hamas that killed at least 1,890 Palestinians and 67 people on the Israeli side, almost all soldiers.
A 10-year-old boy was the first person whom Palestinian emergency services reported killed in Friday's Israeli air strikes in the Sheikh Radwan in northern Gaza City with six others, including a woman, wounded.
The interior ministry and witnesses said warplanes struck targets in Jabaliya in the north, Gaza City and in the centre of the Palestinian enclave. Witnesses also reported artillery shelling east and north of Gaza City.
The Israeli army said it targeted "terror sites" and that Palestinian militants fired 33 rockets at the Jewish state, wounding a civilian and a soldier in the south. Netanyahu ordered the military to retaliate "forcefully to the Hamas breach of the ceasefire", an official said on condition of anonymity.
But efforts to find a longer-term ceasefire in Cairo are ongoing.
The Palestinian delegation remains in Egypt, and although the Israeli delegates returned to Israel on Friday morning, the team has been shuttling back and forth repeatedly in recent days.
Hamas has not claimed responsibility for any of Friday's rocket attacks. Claims instead came from rival armed factions.
In Gaza, some families who had returned home during the truce trickled back to shelter at UN-run schools. At one school in Al-Tuffah in Gaza City, hundreds of refugees were seen living in classrooms, laundry hanging off balconies and a scrum of people queueing for UN food handouts
"Of course we're all scared, I'm scared, my children are scared, my wife is scared," Abdullah Abdullah, 33, told AFP at the school. "I'm afraid because the schools were targeted, because young people died, women and children," he said, referring to UN schools that were hit before the truce.
Israel launched an air campaign on July 8, followed by a ground offensive designed to destroy Hamas's arsenal of rockets and its network of tunnels stretching underground to Israel.
"We will continue to strike Hamas, its infrastructure, its operatives and restore security for the State of Israel," said army spokesman Lieutenant Colonel Peter Lerner.
Rockets before truce expiry
Israel said two Palestinian rockets were fired towards Israel in the hours before the truce expired. In Cairo, Hamas said the Palestinians had refused to extend the ceasefire but confirmed negotiations were continuing Friday.
According to UN figures, at least 1,354 Palestinian civilians were killed in the fighting, including 447 were children.
Hamas has been determined to extract some significant concessions from Israel after such heavy losses. "All the Palestinian factions, including Hamas, have agreed not to renew the ceasefire because (Israel) is refusing to accommodate our demands, but negotiations continue in Cairo," Hamas spokesman Fawzi Barhum told AFP.
The official said members of the Palestinian delegation, which is led by a representative of Palestinian president Mahmud Abbas, would meet after noon to assess their stance.
Israel said this week it was ready to "indefinitely" extend the ceasefire, but a senior Palestinian official accused Israel of procrastinating, warning it could lead to a resumption of fighting. "The Israeli delegation is proposing extending the ceasefire while refusing a number of the Palestinian demands," he said, without elaborating.
Hamas's armed wing, the Ezzedine al-Qassam Brigades, had warned that fighting would resume if their demands were not met, first and foremost to open a sea port to the blockaded Palestinian enclave.
Hamas and Palestine Liberation Organisation (PLO) officials laid out a number of demands, starting with the lifting of Israel's eight-year blockade on Gaza. They also want the release of around 125 key prisoners held in Israeli jails.
Despite the withdrawal of all its troops from Gaza by the time the truce began on Tuesday, Israel has retained forces along the border who are ready to respond to any resumption of fighting.
A British, French and German proposal to rebuild Gaza aims to strengthen the hand of Abbas and his Palestinian Authority while clamping down on Gaza militants to ensure Israel's security.