A full-scale Israeli military operation in Rafah would deliver a death blow to aid programmes in Gaza, where humanitarian assistance remains "completely insufficient", the UN chief warned Monday.

Speaking before the UN Human Rights Council in Geneva, Antonio Guterres said that Gaza's southernmost city, where more than 1.4 million Palestinians are crowded together in tent cities, was "the core of the humanitarian aid operation" in the Palestinian territory.

"An all-out Israeli offensive on the city would not only be terrifying for more than a million Palestinian civilians sheltering there; it would put the final nail in the coffin of our aid programmes," he said.

His comments came after Israeli Prime Minister Benjamin Netanyahu on Sunday reiterated that his country was intent on a ground invasion in Rafah, in its bid for "total victory" over Hamas, whose October 7 attack triggered the war.

He said that once a ground invasion happens, victory would be just "weeks away", and that a potential ceasefire, being discussed in Doha, would only delay the operation.

The war that has been raging for more than four months broke out after Hamas's unprecedented October 7 attack, which resulted in the deaths of about 1,160 people in Israel, mostly civilians, according to an AFP tally of official figures.

Hamas militants also took about 250 Israeli and foreign hostages, 130 of whom remain in Gaza, including 31 presumed dead, according to Israel.

Israel's retaliatory offensive has killed at least 29,692 people, mostly women and children, according to the latest tally issued Sunday by the health ministry in Hamas-run Gaza.

- 'End the bloodshed' -

Guterres stressed Monday that "nothing can justify Hamas's deliberate killing, injuring, torturing and kidnapping of civilians, the use of sexual violence -- or the indiscriminate launching of rockets towards Israel".

"And nothing justifies the collective punishment of the Palestinian people," he said.

Amid a spiralling humanitarian crisis, UNRWA, the main UN aid agency for Palestinians, has urged political action to avert famine in Gaza.

But Guterres stressed that "humanitarian aid is still completely insufficient".

"I repeat my call for a humanitarian ceasefire and the immediate and unconditional release of all hostages," he said.

He lamented that despite his urgent calls for the UN Security Council to take all measures to "end the bloodshed in Gaza and prevent escalation", it had failed to act.

As one of five permanent members of the 15-member council, the United States -- Israel's biggest ally -- has a veto that it has wielded three times so far to bar the body from calling for an immediate ceasefire in Gaza.

Guterres warned of the consequences of the council's lack of action on Gaza, and its failure, due to a Russian veto, to act on the war in Ukraine.

This inaction "has severely -- perhaps fatally -- undermined its authority", he cautioned.

"The council needs serious reform to its composition and working methods."