Israel-Gaza live updates: IDF says it's discovered one of Hamas' biggest tunnels

Dr. Renana Eitan, a psychiatrist who treated people held by Hamas, said some of the now-released hostages experienced "cruelty that I haven't seen before."

"I've been a psychiatrist for over 20 years," she said. "We are [a] national center for sexual trauma and for PTSD for the refugees from Africa, so I thought I saw all the worst PTSD patients."

Some hostages were held "in inhumane sanitary conditions" and "subject to severe physical, sexual and mental abuse," Eitan said.

"I have never seen anything like that before," Eitan said.

"One of the patients, she was kept in total darkness for four days. This is inhumane. She became psychotic. She had hallucinations," Eitan said. "I've never seen such things in my life."

According to the Israel Defense Forces, 137 people are still being held hostage by Hamas.

A group of 18 protesters calling for a cease-fire in Gaza chained themselves to the White House fence on Monday.

The protesters were from Jewish Voice for Peace, a group that defines itself as "Jews organizing toward Palestinian liberation." They chanted, "Biden, Biden pick a side, cease-fire not genocide," and, "Cease-fire cannot wait, no Hanukkah to celebrate."

U.S. Park Police said its officers used bolt cutters to remove the chains from the fencing and cleared the group from the area after roughly 30 minutes.

The demonstration came hours before President Joe Biden holds a Hanukkah reception at the White House.

-ABC News’ Justin Ryan Gomez

The United Nations Relief and Works Agency for Palestine Refugees said 134 of its workers have been killed since the Israel-Hamas war began more than two months ago.

Although northern Gaza was the first region intensely targeted by Israeli forces, the UNRWA said half of its killed staffers died in central and southern Gaza.

There are 1.9 million people now displaced in Gaza, where conditions continue to deteriorate, the UNRWA said.

"Despite everything, our UNRWA colleagues keep going, keep doing everything they can to support their communities," the UNRWA said.

The Israel Defense Forces said its soldiers found explosives, AK-47 rifles and a rocket-propelled grenade hidden inside UNRWA-labeled bags in a home in Gaza.

The IDF said it also found long-distance rockets inside a truck near a school in Gaza.

The Israeli army has "directed aerial strikes on dozens of terrorists in the Gaza Strip” over the last day, the IDF said, and “in one incident, armed terrorists spotted exiting a medical clinic during operational activity were struck by the IDF."