Seventy-four U.S. citizens and family members have crossed from Gaza into Egypt, a senior Biden administration official said, adding that the numbers are fluid and changing in real time.

President Joe Biden said at the White House Thursday, "We got out today 74 American folks, out that are dual citizens, and coming home."

Seventy employees from the United Nations Relief and Works Agency for Palestine Refugees in the Near East have been killed since Oct. 7, the highest number of U.N. aid workers to die in a conflict in such a short time, the agency said.

Israeli troops are operating in Gaza City and are "encircling it from several directions," said chief of the Israeli General Staff, Lt. Gen. Herzi Halevi.

Israeli forces are now also "engaged in a ground operation in the northern Gaza Strip," Halevi said.

Halevi said less than half of the total strength of the Israeli Air Force is operating in the Gaza Strip.

"Most of the force is prepared and ready, with bombs on the wings and people who are ready to be scrambled at any moment to the planes, to go out and strike in other arenas as soon as required," he said.

-ABC News' Jordana Miller

Barbara Zind, a pediatrician from Colorado who was in Gaza working with the Palestinian Children's Relief Fund, said the scene at the Gaza-Egypt border was pure chaos.

"Everyone rushed in and they were pressing the doors," she told ABC News. "They did have a list up of who was on the list to leave."

“People are frustrated. They’re desperate. People are angry. There were a couple of fist fights," she said.

Zind, one of the first five Americans to leave Gaza on Wednesday, said she has survivor's guilt.

"I just left so I might get a little emotional, but these people are just being slaughtered," she said. "These are my friends."

Zind said the bombing was constant.

She said often it was near impossible to contact people outside Gaza. At one point she was in a total communication blackout for 18 hours and unable to tell her husband and son that she was safe.

As conditions worsened, she said at one point they were down to consuming 800 calories per day, with two days left of supplies. She said one man risked his life to drive into Gaza City to get more supplies for everyone to eat for another week.

Zind has made many trips to Gaza to work with children and families there. When asked if she would go back, she said, definitely.

-ABC News' Maggie Rulli

Secretary of State Antony Blinken defended Israel's military actions against Hamas at a Friday news conference in Israel after meeting with Israeli leaders, saying, "This right to self-defense, indeed, this obligation to self-defense, belongs to every nation. No country could, or should, tolerate the slaughter of innocents."

Blinken said during his Friday meetings with Israeli leaders he viewed more footage from Hamas' Oct. 7 attack, describing the videos as "almost beyond the human capacity to process."

In one video, he said, a father at a kibbutz grabbed his two sons, who appeared about 10 or 11 years old, and pulled them from the house into a shelter.

The family was "followed seconds later by a terrorist who throws a grenade into that small shelter," Blinken said.

When the dad came stumbling out of the shelter, he was shot, Blinken said.

The sons then ran from the shelter into the house, crying, "Where's daddy?" he said.

The terrorist then "casually opens the refrigerator and starts to eat from it," Blinken said.

"It is striking, and in some ways, shocking, that the brutality of the slaughter has receded so quickly in the memories of so many. But not in Israel and not in America," he said.

After sharing details of the terror inflicted on Israeli children during the conflict, Blinken touched on the images of young Palestinian boys and girls pulled from the rubble of buildings.

"When I see that, when I look into their eyes through the TV screen, I see my own children," he said.