The Israeli military said it was carrying out a "precise and targeted operation against Hamas in a specified area" of Al-Shifa hospital in Gaza early Wednesday morning. The ground operation, based on intelligence and "operation necessity," came after the Israel Defense Forces (IDF) repeatedly warned Hamas against using the hospital as a base for its operations, the IDF said in a statement.

The IDF said it was "conducting searches for Hamas terror infrastructure and weapons" and delivering "humanitarian aid to the entrance of the hospital."

"Yesterday, the IDF conveyed to the relevant authorities in Gaza once again that all military activities within the hospital must cease within 12 hours. Unfortunately, it did not," the IDF said, adding that Hamas' alleged military use of the hospital was a violation of international law.

CBS News partner network BBC News quoted an eyewitness at the hospital as saying that, once inside the hospital complex, Israeli troops had asked all men between the ages of 16 and 40 who were not in the emergency or surgical departments to gather in the hospital courtyard and pass through a scanning device.

The eyewitness told the BBC that Israeli troops were in complete control of the hospital complex and had gone room to room questioning people. A senior Israeli defense official told reporters, however, that IDF forces were only operating in one specific area of the hospital, though they would not say which one.

Israel's announcement that ground forces were moving in came a day after President Biden said hospitals in the Gaza Strip "must be protected" and voiced his "hope and expectation is that there will be less intrusive action relative to hospitals" in the coastal enclave.

Al Shifa is in the heart of Gaza City and had been at the center of a tense standoff for days. Israel accuses Hamas of having an underground headquarters under the hospital, which both Hamas and doctors at Al Shifa deny.

There's been growing concern for patients at the hospital, which lost power over the weekend due to a lack of fuel for its generators. Israel has not been allowing fuel into the Gaza Strip, claiming it's being hoarded by Hamas.

Dozens of babies had to be removed from their incubators at Al Shifa and they were pictured laid on aluminum foil and blankets for warmth. The IDF said Wednesday that it delivered new incubators to Al Shifa, which it told CBS News could run on battery power for at least a few hours.

Both Israeli and U.S. officials had stressed that Hamas has a long history of positioning weapons and fighters in civilian homes, schools and hospitals. On Tuesday, U.S. National Security Council coordinator for strategic communications John Kirby said the U.S. had "information that Hamas and Palestinian Islamic Jihad use some hospitals in the Gaza Strip, including Al Shifa Hospital, and tunnels underneath them to conceal and support their military operations and hold hostages."

Kirby said Hamas and its allies in the Palestinian Islamic Jihad group were operating a "command and control node" from Al Shifa, adding, "To be clear, we do not support striking a hospital from the air and we don't want to see a firefight in a hospital where innocent people, helpless people, sick people trying to get medical care they deserve are caught in the crossfire. Hospitals and patients must be protected."

The IDF said its forces involved in the operation included medical teams and Arabic speakers "who have undergone specified training to prepare for this complex and sensitive environment, with the intent that no harm is caused to the civilians being used by Hamas as human shields."

IDF spokesperson Lt. Col. Richard Hecht said Wednesday that troops were engaged in a firefight outside the hospital before entering Al Shifa. He said the soldiers were fired on first but added that there had been no deaths confirmed on either side of the exchange.

The Israeli defense official who later briefed reporters said troops had encountered and neutralized four militants as they moved into the complex, and that they quickly found weapons and other evidence that Hamas was, as Israel has long insisted, using the hospital as a terror base. The official said the evidence would be made public.

United Nations humanitarian and health agencies voiced urgent concern Wednesday at the news that the Israel-Hamas ground war was moving onto the grounds of the packed health care facility, with humanitarian relief coordinator Martin Griffiths saying on social media he was "appalled by reports of military raids in Al Shifa hospital" and adding that "the protection of newborns, patients, medical staff and all civilians must override all other concerns. Hospitals are not battlegrounds."

"Hamas must not, should not use a place like a hospital as a shield for their presence. That is as strong a statement under humanitarian law as is the statement that the hospital should not become a place of a war zone, of danger," Griffiths said. "We find these two issues equally important and equally understandable for both sides. Our concern on the humanitarian side is for the the welfare of the patients of that hospital, which is, of course, in great peril at the moment."

World Health Organization director Tedros Adhanom Ghebreyesus called word of the incursion "deeply concerning" and said the U.N. health agency had "lost touch again with health personnel at the hospital. We're extremely worried for their and their patients' safety."

Hamas, which has controlled Gaza for almost two decades, launched an unprecedented terror attacked on Israel on Oct. 7 from the territory, prompting Israeli Prime Minister Benjamin Netanyahu to declare his country "at war." Israel says at least 1,200 people, most of them civilians, were killed in the coordinated, multi-fronted attack and approximately 240 people were taken hostage by Hamas in Gaza.

Netanyahu has said a cease-fire will be possible only if the hostages are released, but Israel's punishing response has divided the international community.

More than 11,070 Palestinians, two-thirds of them women and minors, have been killed since the war began, according to the Hamas-run Gaza Health Ministry, which does not differentiate between civilian and militant deaths. The ministry has said about 2,700 people have been reported missing and many are believed to be trapped or dead under rubble in Gaza, which has been pummeled by Israeli airstrikes since Oct. 7.

The U.N. estimates that some 1.5 million people — more than two-thirds of Gaza's population — have fled the intense fighting in the north of Gaza to head south. Meanwhile, about 250,000 Israelis have been forced to evacuate from communities near Gaza and along the northern border with Lebanon, where Israeli forces and Hezbollah militants have traded fire repeatedly.

Gaza hospital is ‘nearly a cemetery’ amid Israel-Hamas strikes: World Health Organization.

Gaza’s Al-Shifa Hospital is holding about 150 bodies that can’t be removed amid relentless strikes from the Israeli military, the World Health Organization (WHO) and local health authorities claim.

The Israel Defense Forces (IDF) surrounded the hospital Saturday, saying it protects a Hamas militant command post. Hamas and hospital administrators have denied that claim.

“Around the hospital, there are dead bodies which cannot be taken care of or not even be buried or taken away to any sort of morgue,” WHO spokesperson Christian Lindmeier told the BBC. “The hospital is not working at all anymore as it should. It’s nearly a cemetery.”

Hamas said there are roughly 2,000 people inside the hospital, including about 600 patients.

Israel’s military, however, claimed they were fighting Hamas militants in nearby neighborhoods. The IDF added the hospital is not under “siege” and those inside could leave safely — which the hospital’s administrator Dr. Mohamed Abu Selmia contested.

Selmia told the British outlet the Israeli military is not allowing people to leave, including those transporting the bodies, and that dogs entered the hospital grounds and have been seen eating corpses.

Gaza Health Ministry spokesperson Ashraf Al-Qidra said Tuesday that men inside the hospital complex are digging a mass grave for the bodies.

“We are planning to bury them today in a mass grave inside the Al Shifa medical complex. It is going to be very dangerous as we don’t have any cover or protection from the [International Committee of the Red Cross],” he told Reuters. “The men are digging right now as we speak.”

Chief among the concerns of humanitarian organizations is the fate of 36 babies in the hospital’s neonatal ward. Three died Friday after the hospital lost power.

Israel has offered to organize portable incubators to transport the babies, but Al-Qidra said those arrangements have not yet been made.

“We have no objection to have the babies being moved to any hospital, in Egypt, the West Bank or even to the occupation [Israeli] hospitals,” he said. “What we care most about is the wellbeing and the lives of those babies.”

“The occupation is still besieging the hospital and they are firing into the yards from time to time. We still can’t move around, but sometimes doctors are taking the risk when they need to attend to patients,” Al-Qidra added.

Al-Shifa has become the center of fighting in Gaza City amid the Israeli military’s encirclement of the city.

On Saturday, Doctors Without Borders claimed its staff witnessed people being shot at as they attempted to leave the hospital complex.

“Al-Shifa hospital complex … has been hit several times, including the maternity and outpatient departments, resulting in multiple deaths and injuries,” the organization said. “The ambulances can no longer move to collect the injured, and non-stop bombardment prevents patients and staff from evacuating.”

President Biden urged Israel not to fire on hospitals on Monday as negotiations to free about 200 hostages held by Hamas continue.

“My hope and expectation is that there will be less intrusive action relative to hospitals and we remain in contact with the Israelis,” Biden said. “Also there is an effort to get this pause to deal with the release of prisoners and that’s being negotiated. … So I remain somewhat hopeful, but hospitals must be protected.”

The war in the region began early last month after Hamas militants killed more than 1,200 Israelis in a brutal surprise attack on border communities. The responding airstrike campaign and ground invasion of Gaza has killed more than 11,000 Palestinians, including more than 4,000 children.