The union representing American Airlines pilots told its members to "cease flight operations to Israel" amid conflict in the region.

The Allied Pilots Association (APA) president, Ed Sicher, told members to refuse assignments into Israel "until we can be reasonably assured of the region's safety and security."

American Airlines told ABC News earlier Sunday it canceled flight AA145 from Ben Gurion International Airport in Tel Aviv to John F. Kennedy International Airport in New York scheduled for Monday. The carrier said it continues to monitor the situation in Israel and will make further adjustments as needed.

American had announced Saturday it was temporarily suspending operations to and from Tel Aviv and would continue to monitor the situation.

-ABC News' Sam Sweeney, Amanda Maile

Vice President Kamala Harris spoke with Israeli President Isaac Herzog on Sunday to express her and second gentleman Doug Emhoff's condolences and stress U.S. commitment to Israel's security, according to her office.

-ABC News' Fritz Farrow

New York Rep. Dan Goldman and his family were in Israel for a bar mitzvah and on Saturday "sheltered from Hamas rocket fire in their hotel's interiors stairwell until early Sunday," a spokesperson, Simone Kanter, said in a statement.

Goldman and his family were able to safely depart Israel with the help of the State Department and Israeli officials, his spokesperson said.

-ABC News' Lauren Peller

Hospitals in Gaza are "becoming overwhelmed" and are "overcrowded with injured people," Doctors Without Borders/Médecins Sans Frontières said in a statement Sunday.

They're facing a shortage of drugs, medical supplies and fuel for generators, according to MSF, as well as the challenge of safely transporting patients to facilities.

"Ambulances can't be used right now because they're being hit by airstrikes," Darwin Diaz, MSF medical coordinator in Gaza, said.

-ABC News' Cindy Smith

National Security Council spokesperson John Kirby avoided saying if the U.S. believed Israel's calls for civilians in Gaza to evacuate in the next 24 hours was possible but acknowledge that it was a "tall order" given how densely populated the area is.

"Well, I think we're going to be careful not to get into armchair quarterbacking the tactics on the ground by the IDF. What I can tell you is we understand what they're trying to do. They're trying to move civilians out of harm's way and giving them fair warning. Now, it's a tall order. It's a million people, and it's a very urban, dense environment, already a combat zone. I don't think anybody's underestimating the challenge here of affecting that evacuation," Kirby said in an interview on CNN Friday morning.

"But it's pretty clear that what they're trying to do is to the maximum extent possible avoid civilian casualties and also separate Hamas from the human shields. I mean, Hamas actually gave a counterorder telling Palestinians in Gaza to stay at home. Why? Because having human shields, they think, protects them," Kirby continued.

Asked about their efforts to secure a safe passage for civilians out of Gaza, Kirby reiterated that the U.S. is talking to Israel and Egypt but would not comment further on progress.

On the Rafah crossing specifically, Kirby said "So far it's still closed. But that doesn't mean were not going to still try as hard as we can to talk to the Israelis and Egyptians about getting it open and having some sort of safe passage out. It's important that we also continue to work to make sure that humanitarian assistance can get in. The United States has no intention of stopping our efforts to continue to deliver humanitarian assistance, but there has to be a path in, there has to be a path out."

Kirby had no update on the Americans who are believed to be held hostage in Gaza and could not confirm reports that 13 hostages have been killed by Israeli airstrikes, as Hamas has claimed.

-ABC News' Molly Nagle