(AFP) - Israel struck a declared safe zone in Gaza on Tuesday, in a strike the Hamas-run territory's health ministry said killed at least 19 people and the Israeli military said targeted Palestinian militants.

The strike hit Al-Mawasi in the southern Gaza Strip, which Israel had designated as a "humanitarian zone" early in the war, and prompted condemnations from the region and beyond.

Samar al-Shair, one of tens of thousands of displaced Palestinians who have sought refuge in the coastal area, said the attack came "as we were sleeping in our tents".

She told AFP the Israeli military had asked Palestinians to go to Al-Mawasi, "telling us it was safe. Where is the safety?"

Israel has carried out occasional operations in and around the area, including a strike in July that the military said killed Hamas military chief Mohammed Deif, and which Gaza health authorities said left more than 90 people dead.

As mediation efforts again appeared to stall, Israel's Defence Minister Yoav Gallant said a truce and hostage release deal was a "strategic opportunity" that would give his country a "chance to change the security situation on all fronts".

Gallant said that after more than 11 months of war in Gaza, Hamas "as a military formation no longer exists" and has been reduced to "guerrilla warfare".

In Al-Mawasi, the military said it had targeted "significant Hamas terrorists who were operating within a command-and-control centre embedded inside the humanitarian area", which the Palestinian group has denied.

The Gaza health ministry said 19 bodies had been brought to hospitals since the early morning strike, but more victims were probably still buried in the sand.

The territory's civil defence agency earlier gave a death toll of 40, which the Israeli military said did "not align with the information" it had.

- 'Heavy weapons' -

Survivors of the strike scrambled to retrieve belongings from the rubble, including mattresses and clothing, an AFP journalist reported.

The Israeli military said some of the dead were "directly involved in the execution" of Hamas's October 7 attack.

Hamas said claims its fighters had been present at the scene were "a blatant lie".

Civil defence spokesman Mahmud Bassal said people sheltering in the camp in the dunes along the Mediterranean coast had not been warned of the strike, which left "three deep craters".

"There are entire families who disappeared under the sand," he said.

UN chief Antonio Guterres condemned the strike, his spokesman Stephane Dujarric said, adding that "the use of heavy weapons in densely populated areas is unconscionable".

Turkey said the strike added to Israel's "list of war crimes", Egypt denounced "the continuation of Israeli massacres" and Saudi Arabia decried "a new attack in a repeated series of violations by the Israeli war machine".

Arab League ministers, meeting in Cairo, decided to "formally intervene" in support of an International Court of Justice case brought by South Africa that accused Israel of "genocidal acts" in Gaza.

British Foreign Secretary David Lammy condemned "the shocking deaths", which he said showed "how desperately needed" a Gaza ceasefire was.

- Truce efforts stalled -

Following another strike on the Bureij refugee camp in central Gaza, resident Mohammed Awad said: "After 340 days, we've been killed in every way imaginable, we've experienced every kind of death.

"The world hasn't reacted in the past, so what's the point of getting angry or begging now? We have no one but God to help us."

Hamas's October 7 attack resulted in the deaths of 1,205 people, mostly civilians, according to an AFP tally based on official Israeli figures, which includes hostages killed in captivity.

Militants seized 251 captives during the attack, 97 of whom are still held in Gaza, including 33 the Israeli military says are dead.

The Israeli military on Tuesday released footage of a tunnel where it said militants killed six hostages whose bodies were recovered earlier this month.

"They were in this tunnel for weeks or days... in horrific conditions, where there is no air to breathe," military spokesman Daniel Hagari said.

Israel's retaliatory offensive in Gaza has killed at least 41,020 people, according to the territory's health ministry. The UN rights office says most of the dead are women and children.

Elsewhere, the UN's Dujarric said a polio vaccination campaign convoy in Gaza was held at gunpoint at an Israeli checkpoint, shots were fired and its vehicles were rammed by a bulldozer.

He called Monday's incident "the latest example of the unacceptable dangers and impediment that humanitarian personnel in Gaza are experiencing".

The Gaza war has drawn in other Iran-aligned armed groups across the region, with Israeli forces trading regular fire with Hezbollah in Lebanon.

On Tuesday the military and a source close to Hezbollah said an Israeli strike on eastern Lebanon, far from the border, killed a commander from the Iran-backed group.

The war has left large swathes of Gaza in ruins and displaced the vast majority of its 2.4 million people at least once.

"The entire population of the Gaza Strip is now concentrated on 10 percent of the territory," said Philippe Lazzarini, head of the UN agency for Palestinian refugees UNRWA.

© Agence France-Presse