More than 100 aid organisations and human rights groups warned on Wednesday that"mass starvation" was spreading in Gaza, as the United States said its top envoy was heading to Europe for talks on a possible ceasefire and aid corridor.

Israel is facing mounting international pressure over the catastrophic humanitarian situation in Gaza, where more than two million people are facing severe shortages of food and other essentials after 21 months of conflict.

But it denied blocking supplies, saying that 950 trucks' worth of aid were in Gaza waiting for international agencies to collect and distribute.

"We have not identified starvation at this current point in time but we understand that action is required to stabilise the humanitarian situation," an unnamed senior Israeli security official was quoted as saying by the Times of Israel.

On the ground, the Israeli military said it was operating in Gaza City and the north, and had hit dozens of"terror targets" across the Palestinian territory.

Gaza's civil defence agency told AFP that Israeli strikes killed 17 people overnight, including a pregnant woman in Gaza City.

'Wasting away'

The United Nations said on Tuesday that Israeli forces had killed more than 1,000 Palestinians trying to get food since the US- and Israel-backed Gaza Humanitarian Foundation (GHF) started operations in late May – effectively sidelining the longstanding UN-led system.

A statement with 111 signatories, including Doctors Without Borders (MSF), Save the Children and Oxfam, warned that"our colleagues and those we serve are wasting away".

The groups called for an immediate negotiated ceasefire, the opening of all land crossings and the free flow of aid through UN-led mechanisms.

World Health Organization chief Tedros Adhanom Ghebreyesus said on Wednesday that the suffering in Gaza amounted to"man-made" mass starvation.

"I don't know what you would call it other than mass starvation, and it's man-made, and that's very clear," Tedros told a virtual press conference live-streamed from Geneva.

Even after Israel began easing a more than two-month aid blockade in late May, Gaza's population is still suffering extreme scarcities.

Israel says humanitarian aid is being allowed into Gaza and accuses Hamas of exploiting civilian suffering, including by stealing food handouts to sell at inflated prices or shooting at those awaiting aid.

President Isaac Herzog on Wednesday said Israel was acting"according to international law" in Gaza and blamed "Hamas and its people" for "trying to sabotage" aid in a bid to obstruct Israel's military campaign.

GHF said the United Nations, which refuses to work with it,"has a capacity and operational problem" and called for "more collaboration" to deliver life-saving aid.

COGAT, the Israeli defence ministry body that oversees civil affairs in the Palestinian territories, said nearly 4,500 trucks entered Gaza recently, with flour, baby food and high-calorie food for children.

But it said there had been"a significant decline in the collection of humanitarian aid" by international organisations in the past month.

"This collection bottleneck remains the main obstacle to maintaining a consistent flow of humanitarian aid into the Gaza Strip," it added. Aid agencies, though, said permissions from Israel were still limited and co-ordination to move trucks to where they are needed – and safely – was a major challenge.

'Hope and heartbreak'

The humanitarian organisations said warehouses with tonnes of supplies were sitting untouched just outside the territory, and even inside, as they were blocked from delivering the goods.

"Palestinians are trapped in a cycle of hope and heartbreak, waiting for assistance and ceasefires, only to wake up to worsening conditions," the signatories said.

"It is not just physical torment, but psychological. Survival is dangled like a mirage," they added.

"The humanitarian system cannot run on false promises. Humanitarians cannot operate on shifting timelines or wait for political commitments that fail to deliver access."

The head of Gaza's largest hospital said Tuesday that 21 children had died due to malnutrition and starvation in the Palestinian territory over the previous three days.

The United States said its envoy Steve Witkoff will head to Europe this week for talks on Gaza and may then visit the Middle East.

Witkoff comes with"a strong hope that we will come forward with another ceasefire as well as a humanitarian corridor for aid to flow, that both sides have in fact agreed to", State Department spokeswoman Tammy Bruce told reporters.

Mediators have been shuttling between Israeli and Hamas negotiators in Doha since July 6 in search of an elusive truce, with expectations that Witkoff would join the talks as they entered their final stages.

More than two dozen Western governments called on Monday for an immediate end to the war, saying suffering in Gaza had"reached new depths".

Israel's military campaign in Gaza has killed 59,219 Palestinians, mostly civilians, according to the health ministry in the Hamas-run territory.

Hamas's October 7, 2023 attack on Israel, which sparked the war, resulted in the deaths of 1,219 people, most of them civilians, according to an AFP tally based on official figures.