Palestinian health officials said the death toll since July 8 had reached 485, including many civilians, with a woman killed in the predawn strike in Beit Hanoun and 12 more bodies recovered from the embattled Shejaia neighborhood where the number of fatalities rose to 72 from Sunday's fighting.
In its push against militants in Shejaia, Israel also suffered its worst losses in the offensive it launched to stop rocket fire from Gaza at Israel, with 13 soldiers killed, for a total of 18 and another two civilian deaths.
Israel's army said it had been targeting militants from Gaza's dominant Hamas group, charging they fired rockets from Shejaia and built tunnels and command centres there. The army said it had warned civilians two days earlier to leave
The one-day death toll was the highest for the Israeli military's since a 2006 war against Hezbollah guerrillas in Lebanon. It also represented the most Palestinians killed since fighting began on July 8.
The Israeli military said it was checking a televised announcement in Gaza from Hamas's armed wing that it had captured an Israeli soldier during the fighting in Shejaia. Israeli radio, television stations and most news websites ignored the report.
"Qassam Brigades captured a Zionist soldier," said Abu Ubaida on Sunday, the masked spokesman of the Izz el-Deen al-Qassam Brigades, the armed wing of Hamas, who identified the soldier as Shaul Aron and recited what he said was Aron's identity tag number.
He provided no other evidence the soldier was in the custody of the Islamist militants.
Aron would be the first Israeli soldier held captive in Gaza since 2011, when Israel released more than 1,000 Palestinian prisoners to free Gilad Shalit, a soldier who was held for more than five years after his 2006 capture in a cross-border raid.
The bloodshed in Shejaia, the worst for the Palestinians in 12 days of conflict, has touched off renewed Western efforts to seek a truce to resolve the crisis.
Two soldiers killed fighting for Israel were US citizens
Two American men were among the 13 Israeli soldiers killed in the conflict in Gaza on Sunday, the US State Department said, the bloodiest day of the conflict, in which about 100 Palestinians were also killed.
Max Steinberg, a native of California's San Fernando Valley, was a sniper in the Golani Brigade of the Israel Defense Forces, according to a letter sent by the Jewish Federation of Greater Los Angeles to its email list.
Nissim Sean Carmeli, of South Padre Island in Texas, was also fighting in the Golani Brigade, the Houston Chronicle reported.
The US Department of State confirmed both deaths, and said both men were citizens of the United States. It was not immediately clear whether they also held Israeli citizenship. A woman who answered the telephone at a business owned by Carmeli's parents in South Padre Island said they were on their way to Israel on Sunday night.
Seven Palestinian children among 9 killed in Israeli attack: medics
A family of nine Palestinians, including seven children, were killed on Monday by an Israeli airstrike on their home in Gaza, said emergency services spokesman Ashraf al-Qudra.
The deaths bring to 485 the number of Palestinians killed since Israel launched an assault on the Gaza Strip two weeks ago.
US Secretary of State John Kerry was to travel to Cairo on Monday to meet with Egyptian officials about the crisis, U.S.
State Department spokeswoman Jen Psaki said in a statement, adding that the United States was deeply concerned about the risk of further escalation and was pushing for a ceasefire.
Earlier on Sunday, Kerry had said he supported Israel's efforts to destroy tunnels it says Gaza militants use for infiltration attempts and to hide weaponry.
Egypt, Qatar, France and the United Nations have all been pushing, with little sign of progress, for a permanent ceasefire in the worst surge of Israeli-Palestinian fighting in two years.
Qatar was due to host a meeting between Palestinian President Mahmoud Abbas and U.N. Secretary-General Ban Ki-moon on Sunday, and also with Hamas leader Khaled Meshaal, a senior Qatari source told Reuters.
'Open wound' Ban, in Doha, described the fighting in Gaza as an "open wound and we must stop the bleeding now." He was due to travel to Kuwait, Egypt, Israel, the Palestinian Territories and Jordan during the week, a U.N. statement said.
Residents fled Sunday's fighting along streets strewn with bodies and rubble, many of them taking shelter in Gaza's Shifa hospital.
Thousands streamed out of Shejaia, some by foot and others piling into the backs of trucks and sitting on the hoods of cars filled with families trying to get away. Several people rode out of the neighbourhood in the shovel of a bulldozer.
The Shifa hospital director, Naser Tattar, said 17 children, 14 women and four elderly were among 62 Palestinians killed, and about 400 people were wounded in the Israeli assault.
Palestinian fighters kept up rocket fire at Israel on Sunday, though the number of salvoes seemed lower than on previous days.
The Israeli military said 87 rockets were launched from Gaza at Israel on Sunday, and 16 were harmlessly shot down by an Iron Dome interceptor system. The numbers of such shootings have topped 100 on previous days of the offensive.
Israeli Prime Minister Benjamin Netanyahu told a news conference on Sunday evening Israel would press on with its campaign with the goals of "restoring quiet" to its southern cities, and the Tel Aviv business hub area.
Israel also sought to "significantly" damage Hamas and other militant groups' infrastructure in Gaza, he said, adding: "We are undeterred. We shall continue the operation as long as is required."
The Israeli military said it beefed up its presence in Gaza on Sunday, with a focus on destroying missile stockpiles and the vast tunnel system Hamas built along the frontier with Israel.
"I estimate that within two or three days the major part of the tunnels will have been destroyed," Israeli Defense Minister Moshe Yaalon said at the news conference where Netanyahu also spoke.
The UN Relief and Works Agency said that 81,000 displaced people had now taken refuge in 61 UNRWA shelters in Gaza. The Western-backed Abbas in April struck a reconciliation deal with Hamas, which seized the Gaza Strip in 2007 from forces loyal to his Fatah movement. The agreement led to the formation of a Palestinian unity government and Israel's pullout from U.S.-brokered peace talks.