The death toll from tank fire that hit a United Nations shelter in the Gaza Strip‘s main southern city of Khan Younis has risen to 12, a top U.N. aid official said Thursday. Gaza’s Hamas-run Health Ministry said, meanwhile, that Israeli fire had hit a large group of Palestinians waiting to receive humanitarian aid in Gaza City, killing at least 20 people and leaving scores more wounded.

Video obtained and verified by the Reuters news agency showed hundreds of people fleeing amid chaos and the sound of gunfire in Gaza City’s al-Zeitoun neighborhood.  

CBS News could not immediately verify the information provided by the ministry, which does not distinguish between civilian and combatant deaths. The Israeli military said it was looking into the incident.

Gaza City, the largest metropolis in the enclave, was the focus of Israel’s offensive against Hamas for weeks, but the IDF has said the militants were largely driven from the city and the bulk of its operations more recently have been further south, around Khan Younis.

“Twelve people have now been confirmed dead with over 75 injuries, 15 of whom are in a critical condition,” Thomas White, Gaza director of the U.N. agency for Palestinian refugees (UNRWA), said in a statement about the shelling of the agency’s shelter in Khan Younis.

Two tank shells struck the UNRWA shelter Wednesday in Khan Younis, where thousands of displaced Palestinians have taken refuge, White said.

UNRWA chief Philippe Lazzarini said in a post on social media that the bombardment showed a “blatant disregard of basic rules of war,” noting that the compound had been clearly marked as a U.N. facility and its coordinates shared with Israeli authorities.

Asked about the tank fire, the Israeli army said “a thorough review of the operations of the forces in the vicinity is underway,” adding that it was examining the possibility that the strike was a “result of Hamas fire.”

The Israeli army is the only force known to have tanks operating in the Gaza Strip.

The United States also criticized the bombardment, with State Department spokesperson Vedant Patel saying, “we deplore the attack… You’ve heard me say it before, you’ve heard the Secretary say before, but civilians must be protected. U.N. facilities must be respected, and humanitarian workers must be protected so that they can continue providing civilians with the life saving humanitarian assistance that they need.” 

Gaza’s hospitals under siege

CBS News senior foreign correspondent Charlie D’Aagata reported Thursday that in Israel’s relentless assault on Khan Younis, even the city’s hospitals are under siege. Health officials in the Hamas-run Palestinian territory said Thursday that more than 50 civilians were killed over the preceding 24 hours alone, pushing the overall Palestinian death toll in Gaza to almost 26,000 since the war — sparked by Hamas’ brutal Oct. 7 terror attack — began.

In his statement, UNRWA’s Gaza director White said heavy fighting close to the few hospitals still functioning in Khan Younis had “effectively encircled these facilities, leaving terrified staff, patients and displaced people trapped inside.”

He said one hospital, Al Khair, had “shut down after patients, including women who had just undergone C-section surgeries, were evacuated in the middle of the night.” 

“The situation in Khan Younis underscores a consistent failure to uphold the fundamental principles of international humanitarian law: distinction, proportionality and precautions in carrying out attacks. This is unacceptable and abhorrent and must stop. Every measure must be taken to protect civilians. I remind all parties that protection of hospitals, clinics, medical personnel and U.N. premises is explicitly enshrined within international law,” White said.

The Israel Defense Forces said earlier this week that soldiers had surrounded Khan Younis, a Hamas stronghold where the IDF says Hamas militants operate from hospitals and other civilian infrastructure.

Doctors at the biggest health facility in southern Gaza, Khan Younis’ Al Nasser hospital, told CBS News the compound has been surrounded by IDF soldiers over the last week and they fear the troops will raid the facility, where thousands of civilians have sought shelter.

Video shows unarmed man shot dead

There was also a new claim that Israeli soldiers are shooting unarmed civilians in the Palestinian territories. A video clip aired by the British network ITV shows a small group of men waving a white flag in an area Israel designated as a safe zone in southern Gaza. They walk cautiously toward an area they had been forced to evacuate, telling the camera they wanted to find one of the men’s brothers, whom they said had not been permitted to leave by Israeli forces.

As they advance with their hands in the air, there’s a burst of gunfire and one man is shot dead.

The IDF told CBS News it was not aware of the incident, adding: “The video is clearly edited, and we have no way to comment.”

U.K. calls for “immediate humanitarian pause”

U.K. Foreign Secretary David Cameron said Thursday that he had told Israeli Prime Minister Benjamin Netanyahu there should be an “immediate humanitarian pause” in the ongoing fighting between the IDF and Hamas in Gaza, which he said should lead to a permanent cease-fire.

“The scale of suffering in Gaza is unimaginable. More must be done, faster, to help people trapped in this desperate situation,” said Cameron, a former U.K. Prime Minister. He called for Israel to restore water, fuel and electricity supplies to the Gaza Strip, most of which have been cut off or severely limited since the war began on Oct. 7. “We need an immediate humanitarian pause to get aid in and hostages out, followed by a sustainable cease-fire, without a return to hostilities.”

Cameron was to visit Qatar later Thursday to join ongoing negotiations there aimed at increasing the flow of humanitarian aid into Gaza. It has long been hoped that the talks in the Arab nation, which representatives of Hamas and the U.S. have been involved in for weeks, will yield a new agreement to secure the release of the 132 hostages still believed to be held in Gaza.

The negotiations have borne little fruit, however, since a one-week cease-fire in November that enabled the release of 105 hostages, and a leaked remark by Israel’s leader was threatening to complicate the talks further on Thursday.

Netanyahu was allegedly caught on tape telling Israeli hostages’ families this week that Qatar’s mediation was “problematic,” blaming the small nation for funding Hamas.

The Gulf state said it was “appalled” at the remarks, which “if validated, are irresponsible and destructive to the efforts to save innocent lives.”