Another hospital in Gaza, Kamal Adwan Hospital in northern Gaza, is on the verge of closing, with only 20 patients currently getting care, according to Dr. Tedros Adhanom Ghebreyesus, director-general of the World Health Organization.

"This is due to intense fighting as well as a lack of basic supplies: water, food, medicines and fuel," he wrote Wednesday on X, the social media platform formerly known as Twitter.

Nineteen hospitals in Gaza are nonfunctioning, he said. Gaza now has two field hospitals, 14 partially functioning hospitals and three minimally functioning hospitals, Tedros said.

United Nations Secretary-General António Guterres said Wednesday that he's invoked Article 99 of the U.N. Charter for the first time in his six years as leader.

Article 99 says that the secretary-general "may bring to the attention of the Security Council any matter which in his opinion may threaten the maintenance of international peace and security."

"Facing a severe risk of collapse of the humanitarian system in Gaza, I urge the Council to help avert a humanitarian catastrophe & appeal for a humanitarian cease-fire to be declared," Guterres said in a post on X.

In a letter to the U.N. Security Council president, Guterres said, "The situation is fast deteriorating into a catastrophe with potentially irreversible implications for Palestinians as a whole and for peace and security in the region. … The international community has a responsibility to use all its influence to prevent further escalation and end this crisis."

Israeli forces are now "encircling" the house belonging to Yahya Sinwar, the leader of Hamas in the Gaza Strip, Israeli Prime Minister Benjamin Netanyahu said.

"It's only a matter of time until we catch him," Netanyahu said.

The prime minister also said Israel is exerting pressure to allow Red Cross workers to visit the more than 100 hostages still being held by Hamas.

Editor's note: This report contains graphic descriptions of sexual violence.

President Joe Biden has blamed Hamas' refusal to release civilian female hostages for the end of a temporary cease-fire and called reports of women allegedly sexually assaulted by Hamas "appalling."

"We had a report in the earliest days that Hamas used rape to terrorize women and girls during the attack on October the 7th in Israel," Biden said, according to pool reports of his remarks Tuesday at a closed-door fundraiser.

"Over the past few weeks, survivors and witnesses of the attacks have shared the horrific accounts of unimaginable cruelty," he said. "Reports of women raped -- repeatedly raped -- and their bodies being mutilated while still alive -- of women corpses being desecrated, Hamas terrorists inflicting as much pain and suffering on women and girls as possible and then murdering them. It is appalling."

It's on all of us -- government, international organizations, civil society and businesses -- to forcefully condemn the sexual violence of Hamas terrorists without equivocation -- without equivocation, without exception," Biden said.

-ABC News' Libby Cathey

Israeli authorities say they have collated "hundreds of testimonies of rape and sex crimes" they claim was committed by Hamas militants during the Oct. 7 terror attack.

A document from the Israel Defense Forces details allegations of sexual violence, with "almost all of the testimonies" coming from eyewitnesses and first responders who were present at the scene during or after atrocities, the document states. This is because "virtually all" of the victims of sexual violence were also murdered on Oct. 7, according to the document.

The IDF said the document offers "only a small part of an immense body of information of evidence of Hamas' sex crimes" and said the evidence "proves beyond all doubt that Hamas and other … terrorists used rape and sexual violence systemically against Israeli women and children," according to the IDF.

One IDF volunteer quoted in the document described seeing many young women "in bloody, shredded rags, or just in underwear."

"Our team commander saw several (female) soldiers who were shot in the crotch and intimate areas," the IDF volunteer said, according to the document.

The IDF alleges that some members of Hamas who were captured and then interrogated also gave testimony that women were sexually abused on Oct. 7.

An Israeli paramedic quoted in the document said they inspected the bodies of two teenage girls who had been murdered. One of the girls "had her pants pulled down towards her knees ... and there's the remains of semen on the lower part of her back," the document states.

A survivor of the Oct. 7 attack, Gad Liebersohn, quoted in the document said that "for two hours I'm hiding and hearing people getting kidnapped and women getting raped ... begging for their lives."

Hamas, the militant group that governs the Gaza Strip, has denied the allegations that its fighters committed sexual violence during the Oct. 7 attack on neighboring southern Israel.

Cochav Elkayam-Levy, the head of Israel's Civil Commission on Oct. 7 Crimes by Hamas Against Women and Children, has described what she called "widespread rape evidence."

-ABC News' Tom Soufi Burridge