UN Secretary-General Antonio Guterres speaks during a United Nations Security Council meeting on Gaza, at UN headquarters in New York City on December 8, 2023. AFP
Addressing Qatar's Doha Forum, Guterres said the council was "paralysed by geostrategic divisions" that were undermining solutions to the war on Gaza.
The body's "authority and credibility were severely undermined" by its delayed response to the conflict, he said two days after a US veto prevented a resolution calling for a Gaza ceasefire.
"I reiterated my appeal for a humanitarian ceasefire to be declared," he told the forum.
"Regrettably, the Security Council failed to do it," he added.
"I can promise, I will not give up."
Guterres had convened an emergency meeting of the UN Security Council after two months of fighting that have left more than 17,700 people dead in Gaza, most of them women and children.
The secretary-general deployed the rarely-used Article 99 of the United Nations Charter to bring to the council's attention "any matter which in his opinion may threaten the maintenance of international peace and security".
The rule had not previously been invoked by a UN chief in decades.
"We are facing a severe risk of collapse of the humanitarian system," Guterres told the Doha Forum.
"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."