"The entire Palestinian population in North Gaza is at imminent risk of dying from disease, famine and violence," they said in a statement signed by the heads of UN agencies, including the UN children's agency UNICEF and the World Food Programme, and other aid groups.
Israel began a wide military push in northern Gaza last month.
The United States has said it was watching to ensure that its ally's actions on the ground show it does not have a "policy of starvation" in the north.
"Humanitarian aid cannot keep up with the scale of the needs due to the access constraints. Basic, life-saving goods are not available. Humanitarians are not safe to do their work and are blocked by Israeli forces and by insecurity from reaching people in need," they said.
"The situation unfolding in North Gaza is apocalyptic."— United Nations (@UN) UN & civil society leaders urge Israel to cease its assault on Gaza and on the humanitarians trying to help.They reiterate their call to everyone fighting to protect civilians.https://t.co/kLPkhiM87a pic.twitter.com/DhgKU6iP5iNovember 1, 2024
They urged all parties fighting in Gaza to protect civilians and called on Israel to "cease its assault on Gaza and on the humanitarians trying to help".
Israel's UN mission in New York declined comment on the statement.
Israel's UN Ambassador Danny Danon last month told the Security Council that the issue in Gaza was not a lack of aid, saying more than a million tons had been delivered during the past year.
He accused Hamas of hijacking the assistance.
Hamas has repeatedly denied Israeli allegations that it was stealing aid and says Israel is to blame for shortages.
On Monday, the Palestinian Civil Emergency Service said around 100,000 people were marooned in Jabalia, Beit Lahiya and Beit Hanoun in northern Gaza without medical or food supplies.
Reuters could not verify the number independently.
USAID Administrator Samantha Power spoke with Israel's ambassador to the United States on Friday as a deadline imposed by Washington looms for Israel to improve the situation or face potential restrictions on US military aid.
Power and Herzog "discussed the need to get more aid to the Palestinian people," said USAID spokesman Benjamin Suarato.
The United States told Israel in a letter on October 13 that it must take steps within 30 days.
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