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

The Israel Defense Forces said Wednesday morning that its aircraft had bombed "approximately 250 terror targets in the Gaza Strip" over the last day amid what it described as "intensive battles."

"During these strikes, terrorists from the Hamas and Palestinian Islamic Jihad terrorist organizations were eliminated, and a number of terrorist infrastructure were destroyed," the IDF said in a statement.

Israeli soldiers also located "one of the largest weapons depots" in Gaza "near a clinic and a school" in the northern part of the Hamas-controlled territory, according to the IDF.

"The depot contained hundreds of RPG missiles and launchers of various types, dozens of anti-tank missiles, dozens of explosive devices, long-range missiles aimed at central Israel, dozens of grenades and UAVs," the IDF added. "All of the terrorist infrastructure was found close to civilian buildings in the heart of a civilian population. This is additional proof of Hamas' cynical use of the residents of the Gaza Strip as human shields."

Hamas has denied Israel's claims that it deliberately shelters behind civilians in Gaza.

-ABC News' Morgan Winsor

The Israel Defense Forces said Friday morning that it has struck approximately 450 targets in the Gaza Strip over the past day from the air, sea and ground amid "extensive battles with terrorists."

"The troops continue to operate to locate and destroy underground tunnel shafts, weapons, and additional terror infrastructure," the IDF said in a statement.

During operations in Gaza’s southern city of Khan Yunis, Israeli ground troops directed fighter jets "to kill numerous terrorists in a two-hour series of precise strikes," according to the IDF.

Overnight, Israeli warships "used precise ammunition to strike dozens of terror infrastructure sites used by the Hamas naval forces in the central and southern Gaza Strip," the IDF said.

-ABC News' Dana Savir and Morgan Winsor