Three U.S. medical professionals remain in Gaza despite warnings from the U.S. State Department that the American government may not be able to get them out later.

Tamer Hassan, a registered nurse, Dr. Jomana Al-Hinti and Dr. Adam Hamawy were the only ones out of a group of 20 American medical professionals who stayed behind to help treat patients.

"They understand that the U.S. embassy may not be able to facilitate their departure in the same manner as we have just effected today," a person with knowledge of the situation told ABC News.

Hamawy released a statement Saturday explaining why he stayed behind.

"We worry that the European Hospital we currently are in will suffer a similar fate of Al-Shifa and Nasser hospitals, where humanitarian workers, patients, and civilians were massacred," he said.

"To my wife, daughters and son, I know it hurts that I am not coming home this weekend, and I am sorry. But I know that you are proud that I am upholding my oath to never leave anyone behind," he added.

The doctors who left Gaza "made their way to safety with assistance from the U.S. Embassy in Jerusalem," a State Department spokesman said.

-ABC News' Anne Flaherty, Nadine Shubailat and Zoe Magee

Israeli cabinet minister Benny Gantz has given Israeli Prime Minister Benjamin Netanyahu an ultimatum: approve a post-war plan by June 8, or he will resign, Gantz said at a press conference.

"While the Israeli soldiers show supreme bravery on the front, some of the men who sent them into battle behave with cowardice and irresponsibility," Gantz said.

A leader of the National Unity Party and a minister in the war cabinet, Gantz's resignation would not necessarily trigger the collapse of the government on its own, but would be politically significant.

The ultimatum come on the heels of a speech by defense minister Yoav Gallant, who is demanding a plan for the "day after" the war.

-ABC News' Jordana Miller and Dana Savir

Israel announced that it has identified the body of a fourth hostage this week. Ron Benjamin, 53, was killed during the Oct. 7 Hamas attack and taken into Gaza, according to the Israel Defense Forces.

The bodies of three other hostages were also recovered in a tunnel in the same operation, according to the IDF.

Benjamin was a family man who loved cycling, the Hostages Families Forum said in a statement.

"He used to go out for a ride every Saturday, just as he did on that fateful Saturday when he was taken hostage from the Kibbutz Be’eri area while on a cycling trip," the statement said.

-ABC News' Victoria Beaule

More than 630,000 people have fled Rafah since May 6 amid widening operations by Israel’s military, with many seeking refuge in Al-Mawasi and Deir al-Balah -- areas overcrowded with "dire conditions" -- according to the United Nations.

-ABC News' Emma Ogao