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

Hamas announced that it will be delaying the release of Israeli hostages, accusing Israel of violating the cease-fire agreement regarding aid trucks and the agreed-upon terms for the release of Palestinians imprisoned in Israel.

The Al-Qassam Brigades -- the armed wing of Hamas -- said it had decided to delay Saturday's scheduled second round of hostage releases until Israel committed to allowing aid trucks to enter northern Gaza. Hamas was expected to release 13 Israeli hostages in exchange for the release of 39 Palestinians imprisoned in Israel on Saturday, sources told ABC News.

"The Al-Qassam Brigades decides to delay the release of the second batch of hostages until the occupation adheres to the terms of the agreement regarding the entry of relief trucks into the northern Gaza Strip, and due to its failure to adhere to the agreed-upon criteria for releasing prisoners," Al-Qassam Brigades said in a statement.

Hamas leader Osama Hamdan, who is based in Lebanon, said relief trucks that arrived in northern Gaza today were half of the number that was agreed upon.

"There are violations committed by the Israelis in implementing the terms of the truce, some of which occurred yesterday and were repeated today," Hamdan said Saturday, adding that another issue at stake was the reported shooting of two Palestinians on Friday as they tried to reach northern Gaza.

A senior Israeli political source told ABC News that Israel did not violate the agreement. The IDF said about 200 trucks carrying humanitarian aid are expected to enter Gaza today, after 200 trucks with aid entered Gaza yesterday via the Rafah crossing and delivered their cargo to international aid organizations.

The Palestinian Red Crescent said 61 trucks carrying food, water and medical supplies headed to northern Gaza on Saturday, the largest aid convoy to reach the area since the start of the war.

-ABC News' Ayat Al-Tawy, Nasser Atta, Jordana Miller