More than 100 workers with UNRWA, the United Nations agency for Palestinian refugees, have been killed since Oct. 7, the highest number ever seen in a single conflict, the agency said.

Those killed include parents, teachers, nurses and doctors, said Philippe Lazzarini, commissioner-general of UNRWA.

"Devastated. … UNRWA is mourning, Palestinians mourning, Israelis mourning," Lazzarini wrote, again calling for a humanitarian cease-fire.

During brief remarks in New Delhi Friday morning, U.S. Secretary of State Antony Blinken swiftly acknowledged the Biden administration’s “appreciation” of Israel’s commitment to four-hour pauses with three-hour notice in specific areas and corridors of Gaza “that will allow people to move more safely, freely to get out of harm's way and also to access assistance.”

“At the same time, much more needs to be done to protect civilians and to make sure that humanitarian assistance reaches them," he continued. "Far too many Palestinians have been killed. Far too many have suffered these past weeks, and we want to do everything possible to prevent harm to them, and to maximize the assistance that gets to them.”

The secretary said they have established basic principles to guide the effort for lasting peace and security in the region: no use of Gaza as a platform for launching attacks against Israel, no diminution in the territory of Gaza and a commitment to Palestinian-led governance.

Blinken reaffirmed that the administration had “long been committed” to a two-state solution, and the terror attacks of Oct. 7, he said, only redouble American commitment to the peace process.

“But now we've had the events of October 7 -- the almost, beyond the human imagination -- horror of October 7. And I think that only reinforces us in our conviction and our commitment to durable and lasting peace which again, we see through two states,” he said.

On humanitarian assistance, Blinken said that “more than plans, we have a concrete way forward,” including ensuring that there are adequate supplies of fuel for the trucks coming in and that hospitals and desalination plants “have what they need.”

“It's always a process and moving from an understanding, moving from an agreement to implementation is what we're working on right now,” he said.

Any plans for short-term pauses in the fighting in Gaza must be carried out in coordination with the United Nations, said Stéphane Dujarric, spokesperson for the U.N. secretary-general.

The U.N.'s comments come after the White House said Israel agreed to daily four-hour pauses in northern Gaza to allow civilians to escape.

"How any such halt in the fighting, and how it would work for humanitarian purposes, will need to be coordinated with the United Nations, especially on the issue of timings and location," Dujarric said. "And obviously in order for this to be done safely for humanitarian purposes, it would have to be agreed with all parties to the conflict to be truly effective."

Another 65 aid trucks entered Gaza through the Rafah border crossing on Thursday, a border crossing official said.

A total of 821 aid trucks have now crossed into Gaza as the humanitarian crisis worsens.

At least nine Americans remain unaccounted for and U.S. officials believe they are being held hostage by Hamas in Gaza, White House national security adviser Jake Sullivan told ABC News Sunday.

"There are ongoing negotiations involving the Israelis, the Qataris, and we, the United States, are actively engaged in this as well, because we want to make sure that we bring home those Americans who have been taken hostage as well as all of the other hostages," Jake Sullivan told ABC "This Week" co-anchor Jonathan Karl.

Pressed by Karl on the total number of hostages, Sullivan said America doesn't have a "precise number."

"We know the number of missing, and that's the number the Israelis have given. But we don't know how many of those are still alive," Sullivan said. "As far as the Americans are concerned, there are nine missing American citizens, as well as a missing legal permanent representative, a green card holder."

Sullivan said he plans to meet with family members of the American hostages this week.

-ABC News' Fritz Farrow