UN Secretary-General Antonio Guterres issued his harshest rebuke, denouncing as "unacceptable" the killing and injury of starving Palestinians who were trying to access food from non-UN, heavily militarized distribution sites, a spokesperson said on Tuesday.

"The secretary-general condemns the loss of lives and injuries of civilians in Gaza who are once again being shot at while seeking food," said Farhan Haq, the deputy spokesman for Guterres. "It is unacceptable."

This marks Guterres' strongest condemnation of Israel's actions in Gaza to date, underscoring growing international outrage over the escalating humanitarian catastrophe.

More than 338 people had been killed and over 2,800 injured while trying to access food at the Gaza Humanitarian Foundation distribution hubs since the Israel- and U.S.-backed program began in late May, the Gaza Ministry of Health reported.

Haq said the secretary-general continues to call for an immediate and independent investigation into all reports of such killings and for accountability to be established.

The spokesman added that Guterres said all of the October 7, 2023, Israeli hostages held by Hamas must be released immediately and unconditionally. "The secretary-general continues to call for an immediate permanent ceasefire," Haq said.

United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said its humanitarian partners reported that more than 60 people were killed and more than 280 injured on Tuesday alone, some critically, while waiting for aid in Khan Younis. The Israeli military said its troops shot at a crowd and that the incident is under review.

The UN office said casualties were brought to Nasser Medical Complex, where emergency and intensive care units were already overwhelmed, and medical teams were operating with minimal supplies. Some 70 of the injured were referred to field hospitals, primarily to the International Medical Corps' Field Hospital.

Jonathan Whittall, the head of OCHA's occupied Palestinian territory office, is in Gaza and reported the latest mass casualty incident "was part of a chilling pattern where, repeatedly, survivors recount being attacked as they try to reach the aid they need to survive."

OCHA reiterated that civilians must never be targeted, let alone those seeking food amid ongoing starvation.

"Our humanitarian partners continue to report that fuel stocks in Gaza have reached critically low levels," the office said. "Without immediate resupply, essential services, including the provision of clean water, will grind to a halt very soon."

OCHA said that diesel supplies needed to operate critical equipment in southern Gaza are nearly exhausted.

The World Health Organization said that no fuel had entered Gaza for more than 100 days and that attempts to retrieve fuel stocks from evacuation zones were denied by Israeli authorities.

The health agency said that 17 hospitals, seven field hospitals and 43 primary health centers running on minimum amounts of daily fuel will soon have none left.

"The UN and our humanitarian partners call once again for immediate, unimpeded humanitarian access to our aid supplies, to families in the Gaza Strip and to our fuel stocks," OCHA said.

The office said that more Israeli displacement orders compound an already unbearable situation, particularly for children.

It said its partners report that several child protection centers have been forced to close due to these orders, increasing overcrowding in the few that remain operational.

The office said that in the West Bank, Israeli forces intensified strict movement restrictions between Palestinian cities and villages through its network of more than 800 physical checkpoints, gates, roadblocks and other barriers.

"This lockdown has effectively splintered the West Bank, isolating communities from essential services and sources of livelihood," OCHA said, adding that Israeli operations in the northern areas are intensifying, causing further displacement and destruction.

The office said that Israeli forces continued a large-scale raid in Askar camp in Nablus that began on Monday and involved house-to-house searches and arrests. The Israeli authorities informed the Palestinian District Coordination Office that at least 15 residential buildings were to be evacuated ahead of a planned 48-hour operation by Israeli forces. About 75 people were displaced.

(With input from Xinhua)