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
The Israeli military said the civilian casualties were unintentional. It said its jets attacked a tunnel system used by militants, which collapsed, bringing the homes down.
Hamas, the militant group that controls Gaza, called it "pre-meditated killing".
As the U.N. Security Council convened to discuss the worst Israeli-Palestinian violence in years, Prime Minister Benjamin Netanyahu said Israel's campaign in 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 jumped to 192, including 58 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, Israeli authorities say.
At the homes destroyed during the Israeli attack in a Gaza neighbourhood early on Sunday, Palestinians worked to clear rubble from one of the wrecked buildings, recovering 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.
The Israeli military said its aircraft had targeted at a Hamas tunnel system that ran beneath a road in Gaza City.
"The underground military facility collapsed, causing the foundation of the civilian houses above them to collapse as well, leading to unintended casualties," it said in a statement.
The military said it tried to avoid civilian casualties, but said Hamas bore responsibility "for intentionally locating its military infrastructure under civilian houses, thus exposing civilians to danger".
In Gaza, Hamas spokesman Hazem Qassem said: "As usual, Israel is trying to mislead the public opinion through these lies in an attempt to justify the crime and escape responsibility."
Another Hamas official, Sami Abu Zuhri, told Reuters: "What happened this morning was a pre-meditated killing."
Speaking by phone from Istanbul he said: "The images of what happened and from the scene prove that the buildings were targeted directly, which caused them to collapse."
In New York, U.N. 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."
The United States told the Security Council it has made clear to Israel, the Palestinians and others that it is ready to offer support “should the parties seek a ceasefire”.
In his address in Israel, Netanyahu said he wanted to "exact a price from the aggressor" and restore deterrence to prevent future conflict.
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.
The Israeli military said that Hamas, an Islamist group regarded by Israel, the United States and the European Union 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.
NETANYAHU DEFENDS TOWER STRIKE
On U.S. network CBS's "Face the Nation" programme, Netanyahu said Israel had passed information to U.S. 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 has condemned the strike and 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.
U.S. President Joe Biden's envoy, Hady Amr, arrived in Israel on Friday for talks.
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 U.S. 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.