Escalating its bombing campaign, Israel on Sunday began attacking homes of activists in Hamas, the Islamic militant group that rules Gaza. These attacks have led to a sharp spike in civilian casualties, killing 24 civilians in less than 24 hours, a Gaza health official said. Overall, the offensive that began Wednesday killed 91 Palestinians, including 50 civilians.

The rising civilian toll was likely to intensify pressure on Israel to end the fighting. Hundreds of civilian casualties in an Israeli offensive in Gaza four years ago led to fierce international condemnation of Israel.

Hamas fighters, meanwhile, have fired hundreds of rockets into Israel in the current round of fighting, including 12 on Monday, among them one that hit an empty school.

The new airstrikes came as Egypt was trying to broker a cease-fire, with the help of Turkey and Qatar. The Turkish foreign minister and a delegation of Arab foreign ministers were expected in Gaza on Tuesday. However, Israel and Hamas appeared far apart in their demands, and a quick end to the fighting seemed unlikely.

In Monday's violence, a missile struck a three-story home in the Gaza City's Zeitoun area, flattening the building and badly damaging several nearby homes. Shell-shocked residents searching for belongings climbed over debris of twisted metal and cement blocks in the street.

The strike killed two children and two adults, and injured 42 people, said Gaza heath official Ashraf al-Kidra.

Residents said Israel first sent a warning strike at around 2am on Monday, prompting many residents in the area to flee their homes. A few minutes later, heavy bombardment followed.

Ahed Kitati, 38, had rushed out after the warning missile to try to hustle people to safety. But he was fatally struck by a falling cinderblock, leaving behind a pregnant wife, five young daughters and a son, the residents said.

Sitting in mourning with her mother and siblings just hours after her father's death, 11-year-old Aya Kitati clutched a black jacket, saying she was freezing, even though the weather was mild. "We were sleeping, and then we heard the sound of the bombs," she said, then broke down sobbing.

Ahed's brother, Jawad Kitati, said he plucked the lifeless body of a 2-year-old relative from the street and carried him to an ambulance. Blood stains smeared his jacket sleeve.

Another clan member, Haitham Abu Zour, 24, woke up to the sound of the warning strike and hid in a stairwell. He emerged to find his wife dead and his two infant children buried under the debris, but safe.

Clan elder Mohammed Azzam, 61, denied that anyone in his family had any connections to Hamas.

"The Jews are liars," he said. "No matter how much they pressure our people, we will not withdraw our support for Hamas."

Late Sunday, an Israeli missile killed a father and his eight-year-old son on the roof of their Gaza City home. The father, a Hamas policeman, was on the roof to repair a leaking water tank, his relatives said.

In another area of Gaza City, the patriarch of the Daloo family, Jamal, sat in mourning for 11 members of his family killed in a missile strike on his home Sunday. Among the dead were his wife, his son, daughter-in-law, his sister and four grandchildren. His face swollen from crying, he embraced relatives and neighbors paying their condolences.

The mourners sat in plastic chairs just meters away from bulldozers clearing the ruins of Daloo's home. His 16-year-old daughter Yara was still missing and believed under the rubble, family members said.

Daloo, who is left with two sons, tried to take comfort in the belief that the loss of his family was God's will and that the dead are now in paradise. He vehemently disputed Israel's initial claim that a senior operative of Islamic Jihad, a smaller sister group of Hamas, was hiding in his house. He said his son Mohammed, one of those killed, was a policeman in the Gaza police, but not an activist.

"The international public opinion witnessed the facts," he said of the tragedy that befell him. "This does not require my words."

Also Monday, Israel bombarded the remains of the former national security compound in Gaza City. Flying shrapnel killed one child and wounded others living nearby, al-Kidra said. Five farmers were killed in two separate strikes, al-Kidra said, including three who he said had been mistakenly identified earlier by Hamas security officials as Islamic Jihad fighters.

Other strikes killed two fighters on a motorcycle in southern Gaza and two passengers in a taxi that had put a press signs in the windshield, al-Kidra said.

In addition to 91 Palestinians killed over the past six days, some 720 were wounded, al-Kidra said.

On the Israeli side, three civilians have died from Palestinian rocket fire and dozens have been wounded. An Israeli rocket-defense system has intercepted hundreds of rockets bound for populated areas.

Israeli police spokesman Micky Rosenfeld said 12 rockets had struck Israel by late Monday morning, including one that hit a school. Schools in southern Israel have been closed since the offensive started.

Israel launched the current offensive after months of intensifying rocket fire from the Gaza Strip, which continued despite the strikes.

In the night from Sunday to Monday, aircraft targeted about 80 militant sites, including underground rocket-launching sites, smuggling tunnels and training bases, as well as Palestinian command posts and weapons storage facilities located in buildings owned by militant commanders, the Israeli military said in a release. Aircraft and gunboats joined forces to attack Hamas police headquarters, and Palestinian rocket squads were struck as they prepared to fire, the release said.

In all, 1,350 targets in the Gaza Strip have been struck since the Israeli operation began. However, military activity over the past two nights has dropped off as targets change and international efforts to wrest a cease-fire plod ahead.

Israel and Hamas have put forth widely divergent conditions for a truce. But failure to end the fighting threatens to touch off an Israeli ground invasion, for which thousands of soldiers, backed by tanks and armored vehicles, have already been mobilized and dispatched to Gaza's border.

President Barack Obama said he was in touch with players across the region in hopes of halting the fighting. While defending Israel's right to defend itself against the rocket fire, he also warned of the risks the Jewish state would take if it were to expand its air assault into a ground war.

"If we see a further escalation of the situation in Gaza, the likelihood of us getting back on any kind of peace track that leads to a two-state solution is going to be pushed off way into the future," Obama said.