An Israeli air strike in Gaza destroyed several homes on Sunday, killing 42 Palestinians, including 10 children, health officials said, as militants fired rockets at Israel with no end in sight to seven days of fighting.
The Israeli military said the civilian casualties had been unintentional and that it had attacked a tunnel system used by militants, which collapsed, bringing the homes down with it.
As the UN Security Council convened to discuss the worst Israeli-Palestinian violence in years, Prime Minister Benjamin Netanyahu said Israel's campaign in Hamas Islamist-run Gaza was continuing at "full force".
Netanyahu also defended an Israeli air strike on Saturday that destroyed a 12-storey building where the Associated Press and the Al Jazeera TV network had offices. He said the structure also housed a militant group's intelligence office and was thus a legitimate target.
"We are acting now, (and) for as long as necessary, to restore calm and quiet to you, Israel's citizens. It will take time," Netanyahu said in a televised address after meeting with his security cabinet.
The death toll in Gaza overnight jumped to 188, including 55 children, its health ministry said, amid an intensive Israeli air and artillery barrage since the fighting erupted last Monday. Ten people have been killed in Israel, including two children, according to Israeli authorities.
At the homes destroyed during the Israeli attack in a Gaza neighbourhood early on Sunday, Palestinians working to clear rubble from one of the wrecked buildings recovered the bodies of a woman and man.
"These are moments of horror that no one can describe. Like an earthquake hit the area," said Mahmoud Hmaid, a father of seven who was helping with the rescue efforts.
Across the border in the Israeli city of Ashkelon, Zvi Daphna, a physician, whose neighbourhood has been struck by several rockets, described a feeling of "fear and horror".
In New York, UN Secretary-General Antonio Guterres told the Security Council that hostilities in Israel and Gaza were "utterly appalling" and called for an immediate end to fighting.
He said the United Nations was "actively engaging all sides toward an immediate ceasefire" and urged them "to allow mediation efforts to intensify and succeed."
In his address in Israel, Netanyahu said he wanted to "exact a price from the aggressor" and restore deterrence to prevent future conflict.
The Israeli military said that Hamas, an Islamist group regarded by much of the international community as a terrorist movement, and other armed factions have fired more than 2,800 rockets from Gaza over the past week.
This was more than half the number fired during 51 days in a 2014 war between Hamas and Israel, the military said, and more intensive even than Hezbollah's bombardment from Lebanon during the 2006 war between Israel and the Iran-backed Shi'ite group.
Many of the rockets have been intercepted by an Israeli anti-missile system while some have fallen short of the border.
On US network CBS's "Face the Nation" programme, Netanyahu said Israel had passed information to US authorities about Saturday's attack on the al-Jala building. Israel had given advance warning to occupants of the building to leave.
The Associated Press condemned the strike and had asked Israel to put forward its evidence that Hamas was in the building.
There was "an intelligence office for the Palestinian terrorist organization housed in that building that plots and organizes terror attacks against Israeli civilians, so it's a perfectly legitimate target," Netanyahu said on "Face the Nation".
Hamas began its rocket assault on Monday after weeks of tensions over a court case to evict several Palestinian families in East Jerusalem, and in retaliation for Israeli police clashes with Palestinians near the city's Al-Aqsa Mosque, Islam's third holiest site, during the Muslim holy month of Ramadan.
There has been a flurry of US diplomacy in recent days to try to quell the violence, but with little sign of success.
US President Joe Biden's envoy, Hady Amr, arrived in Israel on Friday for talks. Biden spoke with both Netanyahu and Palestinian President Mahmoud Abbas late on Saturday, the White House said.
An official with first-hand knowledge of Amr's meetings in Israel said: "He voiced what the administration has been saying openly about Israel having full US support for defending itself.
"He made clear that no one expects Israel to do otherwise, and that this is clearly not something that can be wrapped up in 24 hours," said the official, who asked not to be identified.
Any mediation is complicated by the fact that the United States and most Western powers do not talk to Hamas as a matter of policy.
And although the militants' rocket campaign is directed against Israel, it has also had the dual effect of marginalising the Western-backed President Abbas - who has been powerless to stop it.
In what Hamas called a reprisal for Israel's destruction of the al-Jala building, Hamas fired 120 rockets overnight, the Israeli military said, with many intercepted and around a dozen falling short and landing in Gaza.
Israelis dashed for bomb shelters as sirens warning of incoming rocket fire blared in Tel Aviv and the southern city of Beersheba. Around 10 people were injured while running for shelters, medics said.
In Israel, the conflict has created anger and polarisation, with violence between communities in mixed Jewish-Arab towns. Synagogues have been attacked and Arab-owned shops vandalised, with Israel's president warning against a slide into civil war.
There has also been an upsurge in deadly clashes in the occupied West Bank. At least 15 Palestinians have been killed by Israeli troops in the West Bank since Friday, most of them during clashes.