A UN agency said Thursday rebuilding war-wracked Gaza will cost an estimated $30 billion to $40 billion and require an effort on a scale the world has not seen since World War II.

"The United Nations Development Programme's initial estimates for the reconstruction of... the Gaza Strip surpasses $30 billion and could reach up to $40 billion," said UN assistant secretary-general Abdallah al-Dardari.

"The scale of the destruction is huge and unprecedented... this is a mission that the global community has not dealt with since World War II."