The United Nations on Thursday launched an emergency appeal for $613 million to help Palestinians recover from Israel's attack on Gaza.

"Help is indeed needed urgently," said U.N. Secretary-General Ban Ki-moon.

Donations will enable the U.N. and other aid organizations to "jump into action to help the 1.4 million citizens of the Gaza Strip to recover," meeting their critical needs for food, clean water, shelter, medicine and restoration of basic services, Ban said.

"The civilian population suffered greatly during three weeks of military operations," he told reporters at the World Economic Forum. "More than one-third of the 6,600 deaths and injured were children and women. As a father of three I was especially troubled by the suffering and trauma that so many families went through."

Ban — the first world leader to enter Gaza since an Israeli blockade of the territory in June 2007 — said failure to act urgently will lead to even greater humanitarian calamity.

"People have lost their families, they have lost their homes, belongings, and livelihoods. Schools, clinics, factories and businesses have been destroyed," he said.

Many people are living amid raw sewage, he said.

Ban said he was encouraged that the United States and some European countries had agreed to try to prevent the smuggling of illicit arms and weapons from the wider region into Gaza again, which otherwise would allow Hamas to use the cease-fire to strengthen itself.

"That's a very serious issue," Ban said.

U.N. humanitarian chief John Holmes said some $92 million of the aid would be delivered in the form of either cash for work or cash assistance.

"We need to deliver the aid very quickly in a way that will actually help to restart the economy and support local markets," Holmes said.

He said the U.N. also needs Israel to keep open all the important crossings into Gaza so that sufficient supplies can be brought in.

"We don't want to go back to the position we had before the fighting started where effectively normal economic and other life in Gaza was being strangled by the restrictions on goods and movement" Holmes said. "For example, no construction materials were able to get through or other key equipment and spare parts.

"Clearly we understand Israel's security concerns, but we believe they can be addressed without sacrificing the basic needs of the population," he said.