GEOFF BENNETT: Now to what is again war in Gaza.

Overnight, Israel began striking targets across Gaza, blaming Hamas for its refusal to release more Israeli hostages prior to negotiations on the second phase of the cease-fire.

But that Israeli hostage demand was not part of the overall cease-fire deal agreed to in mid-January brokered by the Biden administration.

So, tonight, Gaza is again on fire.

William Brangham starts our coverage.

WILLIAM BRANGHAM: In Gaza today, a desperate father races to save his child, another distraught to find his lying in a hospital morgue, and another forced to say his final goodbye lying on a crowded street.

The "News Hour" was at the Al Shifa Hospital, where inconsolable families struggled to make sense of what happened last night.

Mohamed Al Kahlout, whose brother was killed, raged at the Israeli attack.

MOHAMED AL KAHLOUT, Lost Brother to Israeli Airstrike (through translator): How is this an end to a war?

You have dead people all around.

This is injustice.

WILLIAM BRANGHAM: In Khan Yunis, Fedaa Hamdan on the left woke this morning to find her whole family had died.

FEDAA HAMDAN, Lost Family to Israeli Airstrike (through translator): I was asleep, sleeping with my children.

I woke up to find my husband and children dead.

Oh, Arabs, wake up.

Shame on you.

May God punish you, Benjamin Netanyahu.

DR. FEROZE SIDHWA, Trauma Surgeon and Volunteer, MedGlobal: I actually saw some injuries last night that I have never seen in my life.

WILLIAM BRANGHAM: The "News Hour" spoke to Dr. Feroze Sidhwa, who's volunteering with MedGlobal at Nasser Hospital in West Gaza.

He said most of the trauma patients he treated last night were children.

DR. FEROZE SIDHWA: The first patient I saw was, like, maybe a 4-to-5-year-old girl.

She had a devastating brain injury, and I had to tell her father that she was - - because she was barely breathing.

She had multiple pieces of shrapnel to her face and scalp, and she was obviously not going to survive.

WILLIAM BRANGHAM: In 2013, Dr. Sidhwa was a resident surgeon at the Boston Medical Center who treated victims of the Boston Marathon bombing.

DR. FEROZE SIDHWA: This one mass casualty event that we had here overnight would overwhelm literally every hospital in the United States, every single one.

WILLIAM BRANGHAM: Last night's attack ended weeks of relative calm, shattering the fragile cease-fire between Israel and Hamas, a truce that led to the release of 33 Israeli hostages, events which Hamas always staged in Gaza with a theatrical show of defiance.

In exchange, Israel released 2000 Palestinian prisoners and allowed a flood of aid into Gaza during its initial phase.

Hamas says Israel failed to return to the negotiating table, which it says would have led to the return of all remaining hostages.

But Israel says its barrage last night targeted Hamas fighters who were planning further attacks.

LT. COL. NADAV SHOSHANI, IDF International Spokesperson: This is coming after a few weeks where we were identifying indications of Hamas operating on the ground and preparing for some sort of terror attack against our troops, but more severely against our civilians.

WILLIAM BRANGHAM: Israeli Prime Minister Benjamin Netanyahu said these attacks were just the beginning.

BENJAMIN NETANYAHU, Israeli Prime Minister (through translator): From now on, Israel will act against Hamas with increasing intensity.

And from now on, negotiations will only take place under fire.

And I want to assure you, this is just the beginning.

WILLIAM BRANGHAM: Earlier this month, Israel blocked all aid into Gaza and cut water and electricity into the enclave.

And, today, it issued evacuation orders for several areas across the Strip, urging residents to flee immediately.

MAHMOUD FARHAT, Displaced Gazan (through translator): What is the guilt of this child and all these children who spent the whole night in fear, horror and death?

Nothing in our hands to do.

We are powerless.

WILLIAM BRANGHAM: Powerless and displaced once again, residents of Gaza now fear another ground invasion.

For the "PBS News Hour," I'm William Brangham.