At least three premature babies have died at the Al-Shifa Hospital in the Gaza Strip when a missile struck nearby and shut down the medical facility's backup generator, according to a doctor working at the hospital.

Dr. Ahmed Mokhallalti, the chief plastic surgeon at the hospital, told ABC News that the babies died when the power to their incubators was cut off Friday night into Saturday morning.

Mokhallalti said all of the hospital's ventilators were back up and running Sunday, but he expressed fear that more people would die at the hospital due to the relentless bombing.

Hospital officials said two patients in the hospital's intensive care unit also died on Sunday due to complications caused by the shelling.

The international humanitarian group Doctors Without Borders has made repeated calls for the shelling of hospitals in Gaza to cease.

"We are nearly sure that we are alone now. No one hears us," Dr. Mohammed Obeid of Doctors Without Borders said in a video statement from the Al-Shifa Hospital on Saturday.

Obeid said there are about 600 patients at the hospital who need medical care and need to be evacuated.

"The problem is [we need] to be sure we can evacuate the neonatal patients because we have 37 to 40 premature babies," Obeid said. "We have about 17 other patients in the ICU, and we have 600 postoperative patients who need medical care. So the situation is very bad. We need help."

-ABC News' Zoe Magee, Matt Gutman and Sami Zayara

Fighting between Hezbollah and Israeli forces intensified Sunday in southern Lebanon, where the terrorist group has claimed responsibility for launching a series of missile strikes on northern Israel, Israeli military officials say.

“Hezbollah is dragging Lebanon into a war that may happen, and it is making mistakes," Israeli Defense Minister Yoav Gallant said on Saturday. “If it makes mistakes of this kind, the ones who will pay the price are first of all the citizens of Lebanon. What we are doing in Gaza we know how to do in Beirut."

Hezbollah has claimed responsibility for at least five attacks in northern Israel, including one it says resulted in numerous deaths and injuries. The terrorist group also claimed one of its missile strikes targeted Israel's Zarit Barracks on the Israeli-Lebanese border.

Hezbollah has been designated a terrorist organization by multiple countries, including the U.S. and Israel.

Fighting between Hezbollah and Israeli troops intensified Saturday night into Sunday. Local news media broadcast images of the heavy clashes in the hills along the border and smoke rising.

Lebanese Prime Minister Najib Mikati released a statement saying his country does not want war but has made a contingency plan in case it is drawn into the conflict between Israel and Hamas.

"What matters to me is that Lebanon stays away from war and looks forward to stability," Mikati told the Al Jazeera network.

During the Al Jazeera interview, Mikati called for an immediate ceasefire in Gaza.

-ABC News' Marcus Moore

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

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."