The Israeli military has again bombed residential buildings in Beit Lahiya in the Gaza Strip, killing at least 19 Palestinians, as civilians searched for survivors in the besieged northern city after an earlier Israeli strike killed nearly 100 people.

According to the Palestinian Civil Defense in Gaza, the latest Israeli bomb attack hit several Al Louh family homes late on Tuesday evening.

The attack came less than a day after the Israeli military bombed a five-story building belonging to the Abu Nasr family in Beit Lahiya, killing at least 93 people and wounding dozens more. The Health Ministry in Gaza said at least 25 children were among the dead.

The Israeli military said it was “reviewing reports of the attack,” while its main ally, the United States, called the attack “terrible.”

The United Nations Human Rights Office (OHCHR) said it was “appalled” by the bombing, calling it one of the deadliest single attacks in Gaza in nearly three months. The United Nations Humanitarian Aid Agency (OCHA) said the attack on the Abu Nasr family home was one of seven “mass casualty incidents” in Gaza in the past week alone.

Israel's escalating air and ground assault on Beit Lahiya comes as the siege of the northern Gaza Strip enters its 26th day.

The Israeli military said it launched the offensive to prevent the regrouping of Hamas fighters in the territory's north, despite saying earlier this year it had wiped out the Palestinian group – which rules Gaza – in the region.

According to Palestinian Civil Defense, more than 100,000 people in the north are trapped without food or water and dozens remain buried in the rubble of bombed houses, with rescue workers unable to reach them due to Israel's ongoing siege and attacks.

Footage of the Israeli attack on the Abu Nasr family home early Tuesday, shared with Al Jazeera, showed a dust-covered Palestinian trapped under concrete and steel bars while others tried to break apart walls with pickaxes to free him. Outside the building, several bodies wrapped in blankets lay on the ground.

“Martyrs everywhere”

Ismail Ouaida, a witness, said the Israeli attack came without warning.

“As you can see, there are martyrs everywhere,” he said, pointing to two bodies among the rubble. “(There are) corpses hanging over the walls.”

Another Palestinian woman said in footage confirmed by Al Jazeera that she had lost several members of her family.

“My two sons were killed along with their entire families. My unmarried daughter was also killed,” the woman said, crying. “And my other daughter and her five children – all killed. What did they do wrong? What did these innocent people do to be slaughtered like this?”

Rabie al-Shandagly, a 30-year-old survivor, told AFP that most of the victims were women and children.

“The explosion happened at night and I initially thought it was shelling, but when I went out after sunrise, I saw people pulling bodies, limbs and wounded people out from under the rubble,” he said. “People are trying to save the injured, but there are no hospitals or adequate medical care.”

Dozens of wounded people arrived for treatment at Kamal Adwan Hospital, the main medical facility for people in northern Gaza. However, the hospital's director said there were no staff to treat patients because Israeli forces arrested most of his staff in a raid last week.

“Kamal Adwan Hospital and the entire surrounding area is a war zone. The hospital has run out of resources; no medical care; no medical staff. This is because many of our specialist doctors and surgeons have been arrested,” said Dr. Hussam Abu Safiya.

He described chaotic scenes with patients and injured people “strewn all over the hospital floor” and called for urgent international intervention.

USA and UN express concern

In Washington, DC, a US State Department spokesman expressed concerns.

“This was a terrible incident with a terrible outcome,” Matthew Miller told reporters. “We contacted the Israeli government and asked what happened here.”

In Geneva, a spokesman for the UN-OHCHR called for a rapid, transparent and detailed investigation.

“It is imperative for Israel to allow emergency services access to such sites in northern Gaza. In some cases, rescue workers have themselves been attacked while trying to reach the injured,” said Jeremy Laurence.

The UN peace envoy for the Middle East also condemned the attack.

“This horrific attack, alongside a massive displacement campaign in northern Gaza, is another in a deadly series of recent mass casualty incidents that raise serious concerns about violations of international humanitarian law,” Tor Wennesland said in a statement.

“I strongly condemn the widespread killing and injury of civilians in Gaza and the endless displacement of Gaza’s population.”

Israel's years-long war has so far killed at least 43,061 Palestinians in Gaza, most of them women and children, according to Palestinian officials.