GAZA — Israel’s attack has razed buildings and upended families in much of crowded Gaza. But few neighborhoods suffered more than Zeitoun, a district of eastern Gaza City. And few families felt the wrath of the Israeli military more than the Samounis.

Israeli troops swarmed Zeitoun shortly after the ground invasion of Gaza began a week ago, and members of the extended Samouni family said they were moved from house to house as soldiers took over the neighborhood. On Monday, with nearly 100 Samounis huddled together in one house, the shooting and the shelling began, according to accounts of family members and witnesses that were partly corroborated by the Red Cross and the United Nations.

Thirty Samounis died, not all of them quickly. Ahmed al-Samouni, 16, survived.

“I could feel the blood dripping inside my head,” Ahmed said, recalling the days he lay wounded in the bombed-out building. “My father was crawling — he couldn’t move his legs,” he said. His cousin Abdallah, 10, was trying to stand up but kept falling down; his brother Yaqoub, 12, kept removing large pieces of shrapnel from his own stomach; and his sister Amal, 9, was not moving at all. Another brother, Ishaq, 12, was wounded in the legs. He bled for two days before he died.

Ahmed, speaking from his hospital bed, said he wanted to call for help. But his mother, Laila, was among the dead, and her cellphone was nowhere to be found.

The story of the Samouni family has horrified many since Red Cross officials on Wednesday publicized their discovery of four emaciated Samouni children trapped for days in a home with the corpses of their mothers. The Red Cross said the Israeli military denied its paramedics access to the area for several days after the ground invasion began on Jan. 3, part of the offensive against Hamas that Israel says is intended to stop the firing of rockets into southern Israel.

Israeli officials said they were still looking into the Zeitoun episode. A military spokeswoman, Maj. Avital Leibovich, said Monday that the army had “no intention of harming civilians.” Hamas, which governs Gaza, “cynically uses” civilians for cover by operating in their midst, she said.

But some international aid officials are arguing that the plight of civilians in Zeitoun, as well as the shelling of a United Nations school where civilians had sought refuge, should be investigated as war crimes.

“Accountability must be ensured for violations of international law,” Navi Pillay, the United Nations high commissioner for human rights, said in an address in Geneva to a special session of the Human Rights Council focused on Gaza. The council has a reputation for censuring Israel. Ms. Pillay is a respected South African judge who recently assumed the top United Nations human rights job, which is separate from the council.

Ms. Pillay said, “Violations of international humanitarian law may constitute war crime, for which individual criminal responsibility may be invoked.” She suggested that the council weigh dispatching a mission to assess violations committed by both sides.

The Israeli military has not said whether the strike on the house in Zeitoun was intentional or a mistake. In the case of the United Nations school, Israel has said that Hamas militants were firing mortars from a location near the school.

According to Ahmed and other witnesses interviewed at the hospital, soldiers came to several of the Samouni homes that make up a section of Zeitoun soon after the ground invasion started. They told family members to vacate their homes and to gather together in one home down the street. Ahmed said they were moved a second time as well, until nearly 100 of his relatives crowded into one house.

Soldiers searched and occupied the now-empty houses. The Zeitoun neighborhood is strategically located and is known to have many supporters of Hamas. Ahmed said the Israelis wanted to turn it into “a military camp.”

Samouni family members did not deny that Hamas militants operated in the area. A family member said there was no active Hamas resistance in the immediate vicinity, although militants were firing rockets at Israel a little more than a mile away.

At about 6 a.m. on Monday morning, Ahmed said, tanks started demolishing a wall of the house where the extended clan was sheltered. His father moved toward the door, presumably to warn the soldiers that civilians were inside, but the troops started shooting, he said.

The shooting then stopped, and the soldiers appeared to withdraw. But a short time later, three rockets and several shells hit the building and tore apart the rooms where his family was gathered.

Ahmed said he and his brother Yaqoub pulled blankets over their relatives and managed to shut the doors in an attempt to hide from the tanks and soldiers outside. Everyone was crying, he recalled, and he did not immediately realize the scope of the damage.

Some relatives, like Masouda Samouni, 20, Ahmed’s sister-in-law, managed to crawl out by themselves and arrived at the hospital that same day. A few hours after the attack on Monday, she recounted how she had lost her mother-in-law, her husband and her 10-month-old son.

At that time, witnesses and hospital officials believed that 11 members of the extended family were killed and 26 wounded, with five children age 4 and under among the dead. The first survivors who arrived at the hospital may not have been aware of the full extent of the disaster and apparently had not counted all those left behind.

Ahmed, rescued nearly three days later, named 27 relatives who died in the building where he was hiding; the Red Cross said three more corpses were found in a house nearby.

The survivors ate tomatoes, drank water and cooked noodles over a fire, but tried to avoid attracting the attention of soldiers in the area. Relatives who escaped repeatedly asked the Red Cross to send help, but Red Cross officials said their requests to respond to the emergency were rejected by the Israelis during the initial days of the siege.

It was 3:30 p.m. on Wednesday when help finally came, half an hour before the end of a three-hour pause in the fighting ordered that day by Israel to allow humanitarian aid and rescue workers to enter Gaza.

Antoine Grand, the head of Red Cross operations in the Gaza Strip, said in a telephone interview on Thursday that the first rescue team on Wednesday had to leave the dead and take out only the wounded, “horrible as that seems,” because they had only limited time and only four ambulances.

“We had no other choice,” Mr. Grand said.

He added that the ambulances had to stop on one side of an earth mound put up by the military. The team had to walk a mile to the houses and bring back the wounded in a donkey cart.

On Thursday, they went back to the same area and brought out another 103 survivors, three of them wounded.

A report issued by the United Nations Office for Humanitarian Affairs on Thursday, based on telephone interviews with several members of the Samouni family, largely corroborated Ahmed’s version of events, saying about 30 people were killed when the house was shelled repeatedly. The report said the attack on the Samouni home was one of the “gravest incidents” in the Israeli campaign.

In another statement issued on Friday, the humanitarian affairs office emphasized that its report was not intended to render a legal verdict on the attack.

In a rare public statement on Thursday, the Geneva-based International Committee of the Red Cross said it believed that in this instance, the Israeli military failed to meet its obligation under international humanitarian law to care for and evacuate the wounded. The delay in permitting entry to rescue services was “unacceptable,” it said.

The rescue team found “four small children next to their dead mothers in one of the houses,” the Red Cross said. “They were too weak to stand up on their own.”

The Red Cross added that Israeli soldiers were posted at a military position some 80 yards away from the house, and there were several other army positions and two Israeli tanks nearby.

Mark Regev, a spokesman for the Israeli government, said Friday that it was important that “we have better channels of communication and coordination” with the Red Cross and other aid groups. He said Israel had an interest in the Red Cross’s “successfully carrying out its mission.”