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.

—Camilla Schick, Margaret Brennan contributed reporting.

In:
• War
• Terrorism
• Hamas
• Israel
• Gaza Strip
• War Crimes
• Middle East
• Benjamin Neta​nyahu

S. Dev

S. Dev is a news editor for CBSNews.com.