The death toll of Israel’s military campaign in the Gaza Strip rose to 91 Monday, the local Health Ministry said, as shelling and airstrikes continued overnight and into the morning.

Hoping to avert an Israeli ground invasion, foreign leaders stepped up efforts to broker a cease-fire. United Nations Secretary General Ban Ki-moon was en route to Cairo, where he intended to “appeal personally for ending the violence,” a statement from his office said.

Meanwhile, Egypt dispatched Saad al-Katany, the chief of the Muslim Brotherhood’s political party, to lead a delegation to the Gaza Strip on Monday in a show of solidarity for Palestinians living in the besieged enclave.

The Israeli military said in a statement Monday that it struck 80 “terror sites” overnight throughout Gaza, “inflicting severe damage to the rocket-launching capabilities” of militant groups in the Palestinian territory.

Israeli airstrikes on the Gaza Strip on Sunday killed at least 10 members of one family, including a mother and her four children, and struck two buildings used by journalists, inflicting the heaviest toll on civilians since fighting began Wednesday.

Militants in Gaza continued to lob dozens of rounds toward Israel, including two powerful rockets that burst over Tel Aviv on Sunday after Israel’s antimissile system intercepted them in midair.

With little apparent progress in cease-fire negotiations in Cairo, British Foreign Secretary William Hague warned that Israel would lose support from the inter­national community if it followed through on threats to deploy troops in Gaza. President Obama, at the start of a three-day trip to Southeast Asia, reiterated U.S. support for Israel’s right of self-defense but said he was hopeful that the fighting could end through diplomacy.

Egyptian President Mohamed Morsi spoke by telephone Monday to a number of world leaders, according to his spokesman, including German Chancellor Angela Merkel and Iranian President Mahmoud Ahmadinejad.

The Iranian leader commended Morsi’s efforts to stabilize Gaza and said he wanted to “work toward a solution to prevent the continuation of crimes against the innocent sons of Gaza and return security to Gaza and the rest of the Palestinian territories.” according to the Iranian state-run news agency.

The intense crossfire of recent days illustrated the enhanced capabilities that both sides have achieved since a three-week Gaza offensive in 2008-2009, which killed more than 1,400 Palestinians and 13 Israelis.

Since Wednesday, Gaza-based militants have fired about 830 rounds of artillery that either slammed into Israel or were intercepted, according to the Israeli military. The number exceeds the approximately 800 that landed during the earlier Gaza campaign, called Operation Cast Lead.

The handful of longer-range rockets that have been detonated over Tel Aviv and the outskirts of Jerusalem in the past three days mark a game-changer for Hamas, the Islamist group that rules Gaza and in the past has been unable to strike Israel’s largest cities.

Military officials and analysts cautioned that though Israel’s antimissile defense system, called Iron Dome and launched last year, has averted direct strikes on the country’s biggest cities, it is not an ironclad defense. Military officials said Sunday that the radar-equipped system has foiled 85 percent of attacks on populated areas. Late Sunday, the military said Iron Dome had intercepted three more rockets launched from Gaza toward “major population areas.”

“No one thinks that Iron Dome will provide a hermetic defense,” said Capt. Eytan Buchman, an Israeli military spokesman, adding that the threat posed by these new rockets justifies the intense bombardment campaign launched last week with the assassination of a top Hamas commander. “Both in quantity and quality, there’s a significant increase in Hamas’s capabilities,” Buchman said.

Gen. Relik Shafir of the Israeli air force said a cease-fire will be possible only if militants in Gaza stop firing rockets.

“At any given time, we can elevate the level and the type of targets,” he told reporters Sunday night in a conference call. He said Israel has taken “great pains” to avoid civilian casualties but acknowledged that is a difficult task “because Hamas fires from populated areas.”

In Gaza on Sunday, Israeli warplanes dropped bombs that hit the Dallu family residence, killing a mother and her four children, ages 10, 6, 2 and 1, as well as five other relatives. It was the single deadliest strike of the campaign, dubbed Pillar of Defense.

“They killed the whole family,” said Yasser Sallouha, an uncle of the children, looking despondent as he stood near their bodies at the morgue. “The whole family tree is gone. Were the two children launching rockets? I want someone to answer me. They are taking revenge on children.”

On Monday, Gazans buried the Dallu family at the hilltop Sheikh Radwan Cemetery in Gaza City amid continued airstrikes. One explosion shook the hill and sent a cloud of gray smoke into the air over nearby buildings. A few elderly men sobbed as men carried the still bloodied bodies of two of the children.

“We want to be martyrs like them,” Kamal al-Dallu, 60, a cousin of the family, shouted angrily. He said Gaza is ready for an Israeli ground invasion. “We don’t want war, but we will protect ourselves, and we will fight them,” he said.

Dallu and others in Gaza City have reacted with indignation and rage to Israeli warnings to stay away from Hamas or risk getting killed.

“We live in a country that is full of these groups — Hamas, Fatah, and the other factions,” Dallu said. These groups are part of Gaza, and everyone in Gaza is involved, he said. Distance is impossible.

“Where do they have to go?” Ayman al-Sahbani, the head of emergency room at al-Shifa hospital, asked indignantly, referring to the civilians he has treated. “If they say, ‘Go to this specific place; that will be safe,’ just name it.”

Beside him, doctors wheeled in 17-year-old Kafah Thaer on a gurney. She was crying hysterically but had not been wounded. The home next to hers in East Gaza had just been bombed, said Hammam Alloh, an emergency room doctor. “She has psychic trauma,” he said.

Earlier Sunday, Israeli warplanes struck two buildings used by Palestinian and international journalists. Military officials said the targets included an antenna used by militants to communicate and an office dedicated to producing propaganda. Witnesses said six Palestinian journalists were wounded, including a cameraman whose legs had to be amputated.

The Foreign Press Association in Israel issued a letter expressing concern and noting that a U.N. Security Council resolution says that journalists covering conflict must be protected.

“The target was not journalists,” military spokeswoman Avital Leibovich told reporters in Jerusalem. “The journalists in these buildings were serving as human shields for Hamas.”

‘Extracting a heavy price’

The Israeli prime minister hailed the early results of the operation. “We are extracting a heavy price from Hamas and the terror organizations,” Benjamin Netanyahu said Sunday during the opening session of the weekly cabinet meeting. “The army is prepared to significantly expand the operation.”

Officials said Israel targeted more than 50 “terror sites” Sunday, including underground ­rocket-launching sites and tunnels. Israel has activated reservists for a possible ground incursion into Gaza, which could markedly intensify the fighting and increase the death toll.

Arieh Herzog, who formerly led Israel’s missile defense program, said Sunday that militants in Gaza have stockpiled thousands of rockets in recent years. “They are far from finishing their stockpile,” he said. “We can expect if any political decision doesn’t stop this, they can continue fighting for many days.”

Cease-fire negotiations in Cairo appeared to make little headway Sunday, although Hamas’s newly strong standing was underscored as the group’s top leader in exile, Khaled Meshal, met with Morsi and Turkish Prime Minister Recep Tayyip Erdogan.

An Israeli envoy arrived in Cairo on Sunday, the Associated Press reported, citing anonymous Egyptian security sources, but as fighting in Gaza escalated, it was far from clear whether the visit was a prelude to a deal. U.N. Secretary General Ban Ki-moon planned to visit Cairo on Monday to discuss the situation.

Prospect of ground invasion

Recalling the ground invasion during the 2008-2009 conflict, Gaza residents have begun to warily contemplate a new round of street fighting. After prayers at the mosque in the Khan Younis refugee camp in the center of the strip, an imam delivered a fiery sermon filled with local news.

Palestinian fighters had shot down an Israeli Apache helicopter over Gaza City to the north, the preacher announced, the latest in a string of rumors in recent days that have turned out to be false. Each time, though, they have raised the prospect of an imminent ground invasion.

Some in the camp think Hamas is strong enough to deter such a move this time around, said Basil Harb, a university lecturer.

“People say the Israeli troops are afraid of coming into Gaza,” he said.

The angst sometimes gives way to dark humor. Harb said he started to add a new level to the family home last week before the Israeli air offensive started but decided to put the work on hold. “I still need to knock down a wall,” he said, then added with a grin: “I thought about calling the Israelis to send a drone to do it. But what if they sent an F-16 instead and then the whole house would be flattened?”

His brother Sami and their aging mother burst into laughter. But the mood turned dark a moment later. Death has become so normal here, Basil Harb said.

“War, after war, after war,” he lamented.

Hauslohner reported from Gaza. Karin Brulliard in Jerusalem, Reyham Abdul-Karim in Gaza and Michael Birnbaum in Cairo contributed to this report.