The World Health Organization has said Gaza's Nasser hospital has ceased to function following an Israeli raid.
Israel Defense Force (IDF) troops entered the complex on Thursday, saying intelligence indicated hostages taken by Hamas were being held there.
The WHO said it had not been allowed to enter the site to assess the situation.
The IDF has described its operation in Nasser as "precise and limited" and accused Hamas of "cynically using hospitals for terror".
Writing on X, formerly Twitter, WHO head Dr Tedros Adhanom Ghebreyesus said: "Nasser hospital in Gaza is not functional anymore, after a week-long siege followed by the ongoing raid."
"Both yesterday and the day before, the WHO team was not permitted to enter the hospital to assess the conditions of the patients and critical medical needs, despite reaching the hospital compound to deliver fuel alongside partners," he said.
"There are still about 200 patients in the hospital. At least 20 need to be urgently referred to other hospitals to receive health care; medical referral is every patient's right."
The Hamas-run health ministry in Gaza says only four medical staff were left in the hospital trying to care for the remaining patients.
One source inside the hospital, who did not want to be named, told BBC News that 11 patients had died due to interruptions in the supply of electricity and oxygen, and that several doctors had been arrested.
Yesterday, the Israeli military said its troops had been told to keep the hospital running and that food and water had been delivered. Asked about the state of the hospital this morning, an army spokesman said only that they were checking.
Fighting has raged around the Nasser site for weeks. Israel has repeatedly claimed Hamas is using hospitals, along with schools, as operational bases.
The Israeli military says it has killed about 20 Hamas fighters and seized numerous weapons in the area of the hospital.
"Over the past day, dozens of terrorists were eliminated and large quantities of weapons were seized," the IDF said.
At least 1200 people were killed during attacks in Israel by Hamas-led gunmen on 7 October last year.
In response, Israel launched a military campaign in the Gaza Strip. More than 28,400 Palestinians, mostly women and children, have been killed and more than 68,000 wounded since the war began, according to the Hamas-run health ministry.
It added that at least 127 Palestinians have been killed and 205 others injured in the past 24 hours.
- This story was first published by the BBC