Israel-Gaza updates: IDF says it exposed Hamas tunnel under Shifa Hospital

The U.S. and Israel both "do not want to see firefights in hospitals," national security advisor Jake Sullivan said Monday as conditions at Gaza's hospitals worsen.

A Doctors Without Borders surgeon working at Gaza's largest hospital, Al-Shifa Hospital, said when an ambulance was sent outside the hospital gate to bring in patients, the ambulance was attacked.

The surgeon said the medical team has only agreed to leave Al-Shifa if patients are evacuated first.

"We want to see patients protected, we want to see hospitals protected. We have spoken with [the] Israeli government about this, and they have said they share that view," Sullivan said.

Sullivan also said the U.S. is continuing to work on getting fuel to hospitals and allowing evacuations from hospitals if they're in danger.

Twenty people, including babies, have died at Gaza's largest hospital, Al-Shifa Hospital, over the last three day, Ashraf Al-Qidra, spokesman for the Hamas-run Ministry of Health in Gaza, told Al-Jazeera on Monday.

About 1,500 patients and medical staff as well as about 6,000 to 7,000 displaced people sheltering at the hospital have had no medicine, water or food for days, Al-Qidra said.

Al-Qidra said medical staff have been unable to collect or bury decomposing corpses at the hospital courtyard amid constant gunfire and shelling by Israeli forces.

A Doctors Without Borders surgeon working at Al-Shifa Hospital said when an ambulance was sent outside the hospital gate to bring in patients, the ambulance was attacked.

"The medical team agreed to leave the hospital only if patients are evacuated first. We don’t want to leave our patients," the surgeon told Doctors Without Borders. "We need a guarantee that there is a safe corridor. ... If they give us guarantees and evacuate the patients first, we will evacuate."

World Health Organization Director-General Tedros Adhanom Ghebreyesus called the situation "dire and perilous" on Sunday as he again called for a cease-fire.

The Rafah border crossing between Gaza and Egypt opened again on Monday, permitting 559 foreign passport holders as well as Egyptians to cross through to Egypt, a Rafah border crossing official said.

Four injured or sick Palestinians and five of their family members also crossed into Egypt, the official said.

Doctors in the war-torn Gaza Strip are appealing for help from the international community as hospitals run out of life-saving supplies amid Israel's bombardment.

Dr. Hatem Daher, who runs the neo-natal department at Nasser Hospital in Khan Younis in south Gaza, told ABC News that the situation there "is bad."

"There is the difficulty in getting drinking water and washing water, especially in our natal ICU because of the difficulty of getting the fuel for our generator," Daher said.

Daher noted that the situation at the strip's largest medical complex, Al-Shifa Hospital in Gaza City, is even worse. Several doctors from Shifa are now working in Daher's hospital, he said.

"Our colleagues in Shifa Hospital describe a disaster there," Daher told ABC News. "No electricity, no oxygen, no drugs."

Daher warned that dozens of premature babies at Shifa are on the brink of death.

"Because they need incubator, they need electricity, they need oxygen, they will die. All of them," he said. "All of them will die. So, we call this emergency -- emergency call for all world, for all organizations -- WHO, UNICEF, Red Cross, anybody [who] can help these children."

-ABC News' Sami Zayara