The UNâ€™s top humanitarian affairs official has said he was shocked by the â€œgrim and miserableâ€ situation he witnessed on a visit to the Gaza Strip.
Undersecretary General John Holmes said it was the result of Israel closing its border crossings and the â€œlimited food and other materialsâ€ allowed in.
Mr Holmes said 80% of Gazaâ€™s 1.5m population now depended on food aid.
Israeli spokesman Mark Regev said the situation could â€œvery quickly return to where it wasâ€ if rocket attacks ceased.
Israel tightened its blockade of Gaza last month after a sharp rise in rocket attacks by militants based there.
The restrictions prompted militants from the Islamist movement Hamas, which controls Gaza, to blast holes in the border with Egypt on 23 January.
The breaches were sealed by Egyptian security forces only on 3 February, by which time hundreds of thousands of Palestinians had taken the opportunity to cross into Egypt and obtain essential supplies.
As part of a four-day visit to Israel and the Palestinian Territories, Mr Holmes toured the Shifa Hospital, the largest in the Gaza Strip, and the Karni industrial zone near the closed cargo crossing on the Israeli border.
â€œI have been shocked by the grim and miserable things I have seen and heard about during the day,â€ he told reporters at the main UN compound in Gaza City.
â€œ[They] are the result of the current restrictions on the crossings into Gaza, and the very limited amounts of foods and other materials being allowed in.â€
Mr Holmes, who is also the UNâ€™s emergency relief co-ordinator, said the level of goods entering Gaza had dropped to 10% of what it was a year ago.
He said the Israeli restrictions had led to the collapse of the territoryâ€™s economy, which in turn caused widespread unemployment and poverty. As a result, some 80% of Gazans now depended on food aid, he added.
â€œAll this makes for a grim human and humanitarian situation here in Gaza, which means that people are not able to live with the basic dignity to which they are entitled,â€ he said.
â€œSo what is essentially needed is an opening of the crossings, a lot more goods coming in.â€