U.N. agencies are calling for urgency in response to the humanitarian situation in Gaza after the world's leading authority on food crises said Friday that Gaza Strip's largest city is gripped by famine, and that it's likely to spread across the territory without a ceasefire and an end to restrictions on humanitarian aid.

"We are in a race against time," said FAO Director of Office of Emergencies and Resilience, Rein Paulsen during a press briefing Friday. "Every effort must be made for immediate and decisive action to prevent further loss of life and alleviate suffering."

The Integrated Food Security Phase Classification, or IPC, said famine is happening in Gaza City, home to hundreds of thousands of Palestinians, and could spread south to Deir al-Balah and Khan Yunis by the end of next month.

The determination comes after months of warnings by aid groups that Israel's restrictions of food and other aid into Gaza, and its military offensive, were causing starvation among Palestinian civilians, particularly children.

Israel rejected the report, with Prime Minister Benjamin Netanyahu calling it an “outright lie.”

Briefing reporters on Friday, Paulsen, described the conditions of an IPC phase-5: "Livelihoods have collapsed. People's lives and futures have been lost. The social safety nets and networks have been severely disrupted. Widespread malnutrition, untreated illness, collapsing health and food systems, deteriorating water, sanitation and hygiene conditions are all resulting in extreme conditions and excess mortalities."

Also briefing reporters, Samir Elhawary, UNICEF Acting Deputy Director of Emergency Programs, said that the situation is "a real child survival crisis."

"We must collectively act to protect the youngest victims of this conflict. Their survival ultimately depends on the political will to immediately avert what is a man-made crisis," said Elhawary.