UN warns of Gaza aid 'time bomb'
Jan Egeland's comments came as foreign donors met in Stockholm to discuss aid to Palestinians living on restricted aid after Hamas's election victory.
The hosts say they are trying to meet a UN appeal target of $330m (£174m).
On Thursday, donors nearly doubled expectations of aid when they pledged $940m of help to rebuild Lebanon.
About 50 of the countries and organizations which attended Thursday's Lebanon aid conference were expected to stay on to discuss the Palestinian situation.
Earlier this year the U.S. and European Union froze aid to the Palestinian Authority because Hamas has refused to recognize Israel.
A limited flow was later restored, though aid workers say it is not enough.
Living in a cage
Since late June, Israel has also been conducting a large-scale military offensive in the coastal Gaza Strip, after Palestinian militants captured an Israeli soldier.
"The humanitarian situation is critical," Mr. Eliasson was quoted as saying.
Unemployment is high, and in Gaza, the UN says nearly 80% of people live in poverty.
One aid worker who returned from Gaza 10 days ago warned that malnutrition was widespread and many new mothers were unable to breastfeed their babies, reports the BBC's Alix Kroeger in Stockholm.
Instead, they were making up bottles with a third of the recommended measure of formula and topping them up with starch.
The result, the aid worker said, would be lifelong damage to those children. Mr. Egeland also warned that, in the 25 years he had been visiting the Palestinian territories, "I've never seen so much hatred and bitterness as during my last visit there."
He urged both Israel and Palestinian militants to cease hostilities.
"The humanitarian situation is critical," Mr. Eliasson was quoted as saying.