BEIRUT - The U.N. secretary general has issued a stinging rebuke of Israel’s blockade of the Gaza Strip, describing it as an act that has opened the “floodgates of horror” and condemning it as a violation of international law.

“More than an entire month has passed without a drop of aid into Gaza. No food. No fuel. No medicine. No commercial supplies,” António Guterres said in remarks at U.N. headquarters in New York on Tuesday. “As aid has dried up, the floodgates of horror have reopened. Gaza is a killing field - and civilians are in an endless death loop.”

The deadly strikes on Gaza continued Wednesday, with one airstrike in Shejaiya, east of Gaza City, that killed at least 23 people, including eight women and eight children, and injured at least 60 others, according to Gaza’s civil defense agency.

Footage from the scene showed an entire residential building leveled. The Israel Defense Forces said it struck a senior Hamas militant but did provide a name. The explosion was so powerful that one resident, living about 200 meters (about 656 feet) from the strike, said the blast knocked him to the floor. Mass casualty incidents are heaping pressure on hospitals, which are struggling to remain operational amid shortages of medication, surgical supplies, blood units and fuel, doctors say.

Guterres’s comments represent some of the strongest messaging from the United Nations on the dire humanitarian situation in Gaza as U.N. agencies sound the alarm over the severity of the aid shortages brought about by the Israeli-imposed blockade.

Israel banned the entry of all aid into Gaza on March 2 and has said that no aid will enter the war-shattered enclave until the remaining hostages held by Hamas have been released. Aid agencies have slammed the decision as a form of collective punishment.

Israel’s Foreign Ministry rejected Guterres’s statement and accused him of “spreading slander against Israel.”

“There is no shortage of humanitarian aid in the Gaza Strip - over 25,000 aid trucks have entered the Gaza Strip in the 42 days of the ceasefire,” spokesman Oren Marmorstein said in a post on X. “Hamas used this aid to rebuild its war machine. Yet, not a word in your statement about the imperative for Hamas to leave Gaza.”

U.N. officials have denied long-running claims from Israeli officials that Palestinians in Gaza have more than enough food to survive.

The humanitarian situation in Gaza, over a month into the blockade, is reaching a breaking point, aid groups and residents say.

Palestinian civilians have told The Washington Post they are struggling to find affordable food, while doctors have reported having to turn patients away because of a lack of supplies to treat them.

“The situation in Gaza is indescribable. We’ve reached a point where everything - literally everything - is a crisis,” Zekra Abu Qamar, a mother of three in Gaza City, said in an interview Wednesday. “Drinking water is a crisis. Food is extremely scarce. You might find some food in the markets, but the prices are exorbitant.” Most community kitchens had been shut, she added.

All of the bakeries in Gaza supported by the World Food Program were forced to close at the end of March because of a lack of flour and fuel.

According to Gaza’s Health Ministry, by Monday 37 percent of medications and 59 percent of medical supplies had run out.

Medications for operating rooms, intensive care units and emergency departments are depleted to unprecedented low levels, it added in a statement.

Widespread malnutrition across Gaza’s population during the ban on aid entering has left blood unit levels critically low because it has reduced how many eligible donors are in the enclave, the World Health Organization has warned, as the demand for blood to treat injuries continues to rise.

“Life has become almost nonexistent,” Abu Qamar said. “The reality is incredibly harsh. There is poverty, hunger and on top of all that, death and destruction.”

Guterres also used his remarks to reject a new Israeli proposal for a system of monitoring and approving aid entering Gaza.

COGAT, the arm of the Israeli military that coordinates aid, said last week that it met with international aid groups and U.N. agencies to propose “a structured monitoring and aid entry mechanism” for Gaza “to prevent Hamas from seizing humanitarian supplies and to assure organizations’ operations stay neutral and impartial.”

It did not release further details, but Guterres said Tuesday that Israel’s proposals “risk further controlling and callously limiting aid down to the last calorie and grain of flour.”

Guterres said the U.N. would not participate in any arrangement that does not fully align with the humanitarian principles of “humanity, impartiality, independence and neutrality.”

“As the occupying power, Israel has unequivocal obligations under international law,” Guterres said. “The current path is a dead end - totally intolerable in the eyes of international law and history.”

Guterres’s statement was the latest from senior U.N. officials this week criticizing Israel and the wider international community for not doing enough to pressure Israeli authorities into allowing aid to reenter Gaza.

“As UN humanitarian leaders we are repeating unequivocally to the world: we are being deliberately blocked from saving lives in Gaza, and so civilians are dying,” said Tom Fletcher, the U.N. relief chief, said Monday on X as he presented a rare joint statement from himself and the heads of six other U.N. agencies.

“The latest ceasefire allowed us to achieve in 60 days what bombs, obstruction and lootings prevented us from doing in 470 days of war: life-saving supplies reaching nearly every part of Gaza,” the statement said. “While this offered a short respite, assertions that there is now enough food to feed all Palestinians in Gaza are far from the reality on the ground, and commodities are running extremely low.”

It continued: “We are witnessing acts of war in Gaza that show an utter disregard for human life.” Balousha reported from Toronto.