"Civil order is breaking down in Gaza," a UNRWA official said.
The temporary cease-fire between Hamas and Israel ended on Dec. 1, and Israel has resumed its bombardment of Gaza.
The end of the cease-fire came after Hamas freed over 100 of the more than 200 people its militants took hostage during the Oct. 7 surprise attack on Israel. In exchange, Israel released more than 200 Palestinians from Israeli prisons.
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The latest outbreak of war between Israel and Hamas, the Palestinian militant group that governs the Gaza Strip, has passed the four-month mark.
In the Gaza Strip, at least 30,228 people have been killed and 71,377 others have been wounded by Israeli forces since Oct. 7, according to Gaza's Hamas-controlled Ministry of Health.
In Israel, at least 1,200 people have been killed and 6,900 others have been injured by Hamas and other Palestinian militants since Oct. 7, according to the Israel Defense Forces.
There has also been a surge in violence in the Israeli-occupied West Bank. Israeli forces have killed at least 395 people in the territory since Oct. 7, according to the Palestinian Ministry of Health.
The ongoing war began after Hamas-led militants launched an unprecedented incursion into southern Israel from neighboring Gaza via land, sea and air. Scores of people were killed while more than 200 others were taken hostage, according to Israeli authorities. The Israeli military subsequently launched retaliatory airstrikes followed by a ground invasion of Gaza, a 140-square-mile territory where more than 2 million Palestinians have lived under a blockade imposed by Israel and supported by Egypt since Hamas came to power in 2007. Gaza, unlike Israel, has no air raid sirens or bomb shelters.
Israeli ground forces are now operating "in and around" the key southern Gaza city of Khan Younis, an Israeli military official confirmed to ABC News.
The official said the IDF's "intention" was to "encircle" the city and "eradicate Hamas strongholds within it."
-ABC News' Tom Soufi Burridge
National security adviser Jake Sullivan said the U.S. is still having "intensive discussions" with "Israel, Qatar and Egypt about how to best get traction on a strategy that will get all the hostages out."
“The President and I, along with Secretary [of State Antony] Blinken and [CIA] Director [William] Burns, will stay in touch with our Israeli and Qatari counterparts, as well as our Egyptian counterparts, to press Hamas on this issue," Sullivan said. "Right now, Hamas is refusing to release civilian women who should have been part of the agreement. And it is that refusal by Hamas that has caused the end of the hostage agreement, and therefore, the end of the pause in hostilities."
Over 100 people remain hostage in Gaza. National Security Council spokesman John Kirby said Sunday the U.S. thinks "about eight" Americans remain hostage.
"Of course, for the United States, the paramount priority is getting the American hostages out and we are talking to the president about all of his options in terms of securing the release of American hostages," Sullivan said. "Beyond that, I'm not going to comment because we need to be able to have those sensitive, diplomatic discussions behind closed doors."
-ABC News' Molly Nagle
In a heated exchange with a reporter, State Department spokesman Matthew Miller said that while it's proven Hamas deliberately targeted civilians to kill, he said he has not seen evidence that Israel is deliberately killing civilians.
Israel expands ground offensive into all parts of Gaza
"I'm surprised I don't hear more people saying, 'Why doesn't Hamas lay down its arms? Why doesn't Hamas move out of schools?'" Miller said.
At a different point in the briefing, Miller said Secretary of State Antony Blinken told Israeli officials during his recent trip to Israel that the U.S. would like to see more precision and restraint in Israel's operations in southern Gaza, compared to the initial bombardment in northern Gaza, to limit civilian casualties.
"We've seen a much more targeted request for evacuations here, where the Israeli Defense Forces have identified specific neighborhoods where they plan to conduct military operations, and urged in advance of those operations that people in those neighborhoods to move, rather than telling an entire city or an entire region to vacate their homes. So that is an improvement on what's happened before," he said.
Miller added, "They have instructed them to move to areas that we know are deconfliction zones. It's one of the things we discussed with them last week."
-ABC News' Matt Seyler
The women and children freed from captivity in Gaza all lost between 10% to 15% of their body weight, according to Dr. Yael Moze from the Schneider Children's Medical Department.
One family took three showers during their 54 days held hostage, while one child hostage took no shower during all 54 days in captivity, Moze said.
Hostages also suffered psychological abuse, Moze said, recalling one teenager who was allegedly told he'd be held hostage for at least a year.
