Israel Defense Forces troops exposed a 180-foot tunnel 32 feet deep underneath the Shifa Hospital, the IDF and Israel Securities Authority (ISA) said in a joint statement Sunday.

"A deep staircase leads to the entrance of the tunnel shaft, which consists of various defense means including a blast-proof door and a firing hole," the statement continues. "This type of door is used by the Hamas terrorist organization to block Israeli forces from entering the command centers and the underground assets belonging to Hamas. The tunnel shaft was uncovered in the area of the hospital underneath a shed alongside a vehicle containing numerous weapons including RPGs, explosives and Kalashnikov rifles.

"IDF and ISA forces are continuing to uncover the route of the tunnel," the statement adds.

The IDF said it expects to find more tunnels and underground facilities, and that the operation is ongoing and will take some time. About 300 people remain in the hospital, according to the IDF.

-ABC News' Yael Benaya

The World Health Organization confirmed earlier claims by the Palestinian Health Ministry that 31 "very sick" babies were safely transported from Al-Shifa Hospital to another hospital in southern Gaza on Sunday.

The premature infants were evacuated to the Emirates Hospital in Rafah, WHO officials said.

The babies were "clinging to life," the United Nations International Children's Emergency Fund (UNICEF) said in a statement, and their "condition was rapidly deteriorating."

The babies are expected to be transferred to another hospital in Egypt, said Dr. Ashraf al Qwadwa, a spokesperson for the Palestinian Health Ministry. He said nine premature babies have died since the start of a fuel crisis in Gaza prompted by the ongoing conflict.

Six health workers at the Al Shifa Hospital and 10 family members of staff there were also evacuated on Sunday along with the babies, according to the WHO statement, adding that further missions are planned to "urgently transport" the remaining patients and health staff out of the hospital.

-ABC News' Nasser Atta

A British-owned cargo ship operated by a Japanese company was hijacked by Houthi militants near Yemen in the southern Red Sea, officials said Sunday.

The Israel Defense Forces released a statement describing the hijacking as a "very grave incident of global consequence."

"The ship departed Turkey on its way to India, staffed by civilians of various nationalities, not including Israelis," the IDF said. "It is not an Israeli ship."

Israeli Prime Minister Benjamin Netanyahu's office called the incident an "Iranian attack on an international ship," adding the vessel was "hijacked on [an] Iranian whim by the Houthi militia in Yemen."

Netanyahu's office confirmed that no Israelis were on the ship, saying the 25-person crew was of different nationalities, including Ukrainians, Bulgarians, Filipinos and Mexicans.

The Houthi militant group is expected to hold a news conference, a spokesperson for the group said.

A spokesman for Yemen's Iran-aligned Houthi military, Yahya Sarea, had said earlier Sunday the group would target all ships owned or operated by Israeli companies or carrying the Israeli flag, according to the group's Telegram channel.

-ABC News' Nasser Atta, Jordana Miller and Dana Savir

Negotiations to free the more than 200 hostages believed to be held by Hamas in Gaza have "reached a very sensitive stage" as some of the key areas of disagreement have "narrowed," a top White House official told ABC's "This Week" on Sunday.

Jon Finer, deputy national security adviser to the White House, suggested that a breakthrough in the negotiations could be imminent.

"These talks have clearly reached a very sensitive stage," Finer told "This Week" co-anchor Martha Raddatz. "We’re following this minute by minute, hour by hour, and have been over a number of weeks. And this is an incredibly high priority for all of us in this administration up to and including, certainly, the president."

Amid new reporting by The Washington Post that an agreement is on the verge of being struck for dozens of captives to be released in exchange for a pause in the fighting, Finer said progress was being made but cautioned that the work was not done.

-ABC News' Tal Axelrod

President Joe Biden said Friday that the release of 24 hostages held by Hamas in Gaza is "just the beginning" of a plan to free 50 of the more than 230 captives over four days.

“It's only a start, but so far it's gone well,” Biden said in a televised address from Nantucket, Massachusetts, where he and first lady Jill Biden are vacationing.

He said Friday's hostage release is part of a deal "reached by extensive U.S. diplomacy, including numerous calls I've made from the Oval Office to leaders across the region," including calls with Israeli Prime Minister Benjamin Netanyahu, Egyptian President Abdel Fattah El-Sisi and the emir of Qatar.

“All of these hostages have been through a terrible ordeal, and this is the beginning of a long journey of healing for them,” Biden said. “Today has been a product of a lot of hard work and weeks of personal engagement.”

Biden said that under the deal, more hostages would be released over the next three days with 50 being "our goal." But he added, "We also will not stop until we get these hostages brought home and an answer to their whereabouts.”

The president said U.S. officials do not know when Americans -- including two women and 4-year-old Abigail Edan, whose parents were killed by Hamas terrorists -- will be among those that are released or their conditions. He added, “We expect it to occur” and that it’s his “hope and expectation” that it “will be soon.”

Biden said the four-day cease-fire that was negotiated for the release of the hostages will allow time to "accelerate and expand humanitarian assistance going into Gaza."

Speaking of the children freed on Friday, one just 2 years old, Biden said, “The teddy bears waiting to greet those children at the hospital are a stark reminder of the trauma these children have been through at such a very young age.”

-ABC News' Justin Gomez