Vice President Kamala Harris and second gentleman Doug Emhoff spoke with the parents of Hersh Goldberg-Polin, an American-Israeli hostage who was found dead in Gaza on Saturday along with five other Oct. 7 hostages, according to the Israel Defense Forces.

The vice president and her husband called parents Rachel Goldberg and Jon Polin on Sunday to "express our condolences following the brutal murder of their son by Hamas terrorists," Harris said in a statement on X.

"My heart breaks for their pain and anguish," Harris continued.

"I told them: As they mourn this terrible loss, they are not alone. Our nation mourns with them," Harris said.

Protesters took to the streets of Tel Aviv Sunday night, demanding a cease-fire agreement and the release of the remaining hostages being held by Hamas terrorists.

The demonstration came a day after Israel Defense Forces recovered the bodies of six hostages in tunnels under the city of Rafah in the Gaza Strip.

Protesters were seen waving Israeli flags as they demanded a cease-fire agreement, chanting "Deal. Now."

-ABC News' Victoria Beaule

At least six people were killed on Sunday when Israel Defense Forces conducted an airstrike on a school in Gaza City, according to Gaza Civil Defense.

The IDF said in a statement that the strike was aimed at Hamas terrorists they allege were operating a command-and-control center inside the Safad school to plan and carry out terrorist attacks against the IDF and Israel.

"Prior to the strike, numerous steps were taken to mitigate the risk of harming civilians, including the use of precise munitions, aerial surveillance, and additional intelligence," the IDF said in a statement.

The Gaza Civil Defense confirmed the Safad school was hit in the IDF strike, but said the school houses displaced people from the Al-Zeitoun area east of Gaza City.

-ABC News' Victoria Beaulé

Secretary of State Antony Blinken spoke Sunday with the parents of U.S.-Israeli citizen Hersh Goldberg-Polin, who Isreal Defense Forces found fatally shot Saturday along with five other hostages who were being held in Gaza tunnels by Hamas terrorists, according to a State Department spokesperson.

In his phone conversation Sunday with Rachel Goldberg and Jon Polin, Blinken offered "deep condolences for the death of their son," said State Department spokesperson Matt Miller said.

-ABC News' Shannon Kingston

The six hostages whose bodies were recovered Saturday in Gaza appeared to have died "shortly before" they were found, the Israeli military said Sunday.

"According to the initial assessment we have, they were brutally murdered by Hamas terrorists shortly before we reached them," Rear Adm. Daniel Hagari, an Israel Defense Forces spokesperson, said on Sunday.

The bodies were discovered in a tunnel in Rafah, the densely populated border city in southern Gaza, Hagari said. They were found about a kilometer from where Farhan Al-Qadi, another hostage, was rescued days earlier, he added.

"Since the location of Farhan Al-Qadi, the forces have been given emphasis on careful and controlled action, even more than usual, with the understanding that there may be other abductees in the area," Hagari said. "We did not have information about the exact location of the abductees."

Fighting between Israel and Hamas had been ongoing on Saturday above ground in the area where the bodies were discovered, he said.

The families of hostages released on Sunday a statement mourning the dead and condemning the Israeli politicians who they said they believe are slow-walking and blocking a cease-fire and hostage-return deal.

"A deal for the return of the hostages has been on the table for over two months," the statement said. "Were it not for the delays, sabotage, and excuses those whose deaths we learned about this morning would likely still be alive."

-ABC News' Jordana Miller, Anna Burd, Victoria Beaule and Kevin Shalvey