“Gaza is currently kept alive through external funding and the illegal tunnel economy,” the United Nations report said, referring to the vast network of smuggling tunnels under the Gaza-Egypt border.

“With little room for further growth,” it added, “Gaza needs to be open and accessible to the world.”

Despite some economic growth last year, 80 percent of Gaza households receive some form of assistance, according to the report, and 39 percent of the residents live below the poverty line. Unemployment was 29 percent in 2011. The report said many Gazans faced food insecurity, primarily because of poverty rather than a shortage of food.

To maintain current educational and health care standards, Gaza will need an additional 440 schools by 2020 and an additional 800 hospital beds.

The enclave, which already faces regular power shortages, will need to double electricity provisions to meet demand by 2020, the report added. And with Gaza’s only aquifer already endangered, it said, a “huge investment” is required in water and sanitation infrastructure, including long-term solutions like the construction of large-scale seawater desalination plants.

Mohammed Awad, Hamas’s minister of planning, said the report did not take into account the positive changes that Hamas brought to Gaza, including increased security and “good governance.” He also said it did not emphasize the degree to which the blockade was responsible for the lack of development.

“The siege obstructed many development projects, especially those related to water,” he said. “The report should have called for and recommended achieving stability in the region so our government would be able to implement its development plans.”

An Israeli official said that Israel, the Palestinian Authority and the international community were working on several fronts to try to improve the situation in Gaza. Speaking on condition of anonymity because the Israeli government did not respond formally to the report, he said Israel had offered to sell more water to Gaza, but that the proposal was awaiting the agreement of the Palestinian Authority. Israel does not deal directly with Hamas.