Israel-Gaza live updates: 3 premature babies die at Al-Shifa Hospital, doctor says

At least nine Americans remain unaccounted for and U.S. officials believe they are being held hostage by Hamas in Gaza, White House national security adviser Jake Sullivan told ABC News Sunday.

"There are ongoing negotiations involving the Israelis, the Qataris, and we, the United States, are actively engaged in this as well, because we want to make sure that we bring home those Americans who have been taken hostage as well as all of the other hostages," Jake Sullivan told ABC "This Week" co-anchor Jonathan Karl.

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US is ‘actively engaged’ in ongoing hostage negotiations: Jake Sullivan

ABC News’ Jonathan Karl interviews National Security Adviser Jake Sullivan on “This Week.”

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Pressed by Karl on the total number of hostages, Sullivan said America doesn't have a "precise number."

"We know the number of missing, and that's the number the Israelis have given. But we don't know how many of those are still alive," Sullivan said. "As far as the Americans are concerned, there are nine missing American citizens, as well as a missing legal permanent representative, a green card holder."

Sullivan said he plans to meet with family members of the American hostages this week.

-ABC News' Fritz Farrow

The World Health Organization announced early Sunday morning that it had lost communication with its contacts in Al-Shifa Hospital in northern Gaza.

Al-Shifa Hospital, the largest medical complex in Gaza, has been under attack in the last 48 hours, according to WHO.

The last report WHO says it received from staff within the hospital said Al-Shifa was surrounded by tanks and there was a "lack of clean water and risk of the last remaining critical functions, including ICUs, ventilators and incubators, soon shutting down due to lack of fuel."

Dr. Ahmed Mokhallalati, the chief plastic surgeon at Al Shifa hospital in Gaza, told ABC News that he is unwilling to leave his scores of burn patients and stayed behind with the some 2,000 people left in the hospital complex and about 500 patients.

Mokhallalati said the hospital is virtually cut off because no one can get in -- they only received two or three patients on Saturday.

But despite having hundreds of burn patients, Mokhallalati doesn’t have much to do because they have only enough power for a single outlet to work. They use it in a clinic which has become the only operating room, because the real ORs require more power.

Mokhallalati said only about 15-20% of the hospital staff remain.

He also said there are some 40 infants in the neonatal units and 60 or so patients on ventilators, who he and the hospital administrators say will die once the generator fuel runs out.

The Israeli military’s civil coordinator said in a video statement Saturday that the eastern exit to the hospital is open, and that people are free to leave. But the images the Israeli military released from inside Gaza show that much of Gaza City and it’s outlying neighborhoods are flattened.

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Gazans flee as new strikes hit hospitals

The World Health Organization says it has verified over 250 attacks on hospitals, ambulances, clinics and patients in Gaza since the war started.

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-ABC News' Matt Gutman and Sohel Uddin

Hezbollah issued two statements claiming two attacks on Israel amid daily clashes between Hezbollah and Israel forces along Lebanon’s southern border.

For the first time since the Oct. 7 Hamas attacks, the Israel Defense Forces said it carried-out a strike 40 km past its northern border into Lebanon, hitting a truck in Zahrani.

For now, this is contained within the the Blue Line, the UN-defined demarcation line between the two countries. As the fighting continues between Hamas and Israel and casualties mount up, the potential for escalation increases.

All of this is happening ahead of the commemoration of Hezbollah’s Martyr Day and another speech by Hezbollah Secretary General Hassan Nasrullah, his second of the conflict.