The head of the UN agency for Palestinian refugees warned Wednesday of the risk of famine in Gaza, a day after the United States said Israel had been warned to improve aid deliveries to the territory.

UNRWA chief Philippe Lazzarini told a press conference in Berlin that "there is a real risk today... that we enter a situation where famine or acute malnutrition is unfortunately again a likelihood," pointing to the upcoming winter and the weakened immune systems of Gaza's population.

Vast areas of Gaza have been devastated by Israel's retaliatory assault on the territory after the October 7 attack last year by Hamas.

Israel has been intensifying operations in the north of the besieged Palestinian territory, where the UN has warned hundreds of thousands of people are trapped.

Lazzarini painted a dire picture of the humanitarian situation in Gaza, saying it had "become a kind of wasteland, which I would say is almost unliveable".

In relation to aid deliveries to Gaza he said that "over the last two to three weeks there was no convoy entering into the north except yesterday".

"We have a huge drop of convoys in the south with only an average of fifty to sixty for two million people, while we estimate the number needed much, much higher," Lazzarini said.

He pointed out that the convoys which had managed to enter had been subject to looting "because of the total breakdown of law and order".

However, he stressed that with appropriate action a hunger crisis in Gaza "can be avoided" if convoys and food are allowed to enter.

"We have shown that we can have a polio campaign, so why can we not bring food?" he asked.

The US State Department on Tuesday said Secretary of State Antony Blinken and Defense Secretary Lloyd Austin sent a joint letter making "clear to the government of Israel that there are changes that they need to make again to see that the level of assistance making it into Gaza comes back up from the very, very low levels that it is at today".

On Wednesday, Austin spoke with Israeli counterpart Yoav Gallant and encouraged Israel to "continue taking steps to address the dire humanitarian situation," according to a Pentagon readout of the call.

COGAT, the Israeli military body supervising civilian affairs in Palestinian territories, said on Wednesday that "50 trucks carrying humanitarian aid -- including food, water, medical supplies, and shelter equipment provided by Jordan -- were transferred today to northern Gaza".

Commenting on the issue of aid flows into Gaza, Israel's ambassador to the UN Danny Danon said Wednesday that "the problem in Gaza is not lack of aid", adding: "The problem is Hamas, which hijacks the aid, stealing, storing and selling it to feed their terror machine, while civilians suffer."

Israeli Foreign Minister Israel Katz told Germany's Bild newspaper on Wednesday that "we are doing everything to let the international community supply humanitarian aid to Gaza."

"I think that we did, and (are) doing more than any other country ever did for their enemies," he said.