The head of the United Nations children's agency on Wednesday called the besieged Gaza Strip "the most dangerous place in the world to be a child," and said that the hard-won truce deal between Israel and Hamas was not enough to save their lives.

UNICEF's executive director Catherine Russell told the UN Security Council that over 5,300 children have reportedly been killed in Gaza since Hamas' October 7 attack on Israel, accounting for 40 percent of the deaths.

"This is unprecedented," said Russell, who had just returned from a trip to southern Gaza. "I am haunted by what I saw and heard."

Russell welcomed a deal reached Wednesday by Israel and Hamas to free hostages and pause ferocious fighting and bombardment in Gaza.

Some 240 people -- ranging from infants to the elderly -- were taken captive during the October 7 attack by Hamas militants that killed about 1,200 in Israel, mostly civilians, according to Israeli authorities.

But Russell said that a pause is not enough and called for "an urgent humanitarian ceasefire to immediately put a stop to this carnage."

"For children to survive..., for humanitarian workers to stay and effectively deliver..., humanitarian pauses are simply not enough," she said.

Russell said that an additional 1,200 children are believed to remain under the rubble of bombed-out buildings or are otherwise unaccounted for.

"In addition to bombs, rockets, and gunfire, Gaza's children are at extreme risk from catastrophic living conditions," Russell added.

"One million children -- or all children inside the territory -- are now food insecure, facing what could soon become a catastrophic nutrition crisis."

UNICEF estimates that acute malnutrition in children could increase by nearly 30 per cent in Gaza over the next months.

Also addressing the Security Council, the head of the United Nations Population Fund, Natalia Kanem, drew attention to the plight of Gaza's pregnant women, with some 5,500 expected to deliver babies under appalling conditions in the coming month.

"At a moment when new life is beginning, what should be a moment of joy is overshadowed by death and destruction, horror and fear," said Kanem.

Sima Bahous, who leads another agency, UN Women, said that girls and women were facing unheard-of dangers.

According to Bahous, 67 percent of those killed in Gaza so far have been women and children. "That is two mothers killed every hour and seven women every two hours," she said.

"We have witnessed six rounds of violence in Gaza in the past 15 years, yet the ferocity and destruction that the Gazan people are being forced to endure under our watch has reached an intensity we have never seen before," she said.

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