GAZA CITY, Gaza Strip — The Gaza Strip will soon become entirely dependent on foreign aid and face "disastrous consequences" if the Hamas-run territory remains sealed off, the U.N. warned on Thursday.

A Palestinian business group, meanwhile, estimated that at least 120,000 Gazans could lose their jobs if the closure continues.

Israel and Egypt closed their crossings with Gaza to all but humanitarian aid after the Islamic militant group Hamas violently seized power in the coastal strip in June, exacerbating the poverty among the 1.4 million residents.

However in a special case, Israel on Thursday allowed the last of more than 6,300 Palestinians stranded in Egypt since the closure to return home to Gaza. The military said the last 475 crossed the Egypt-Israel border at Nitzana in the Negev desert, and were then escorted to the Israel-Gaza border at Erez, about 43 miles to the north to end an 11-day operation.

The blockade has put Gaza's fragile economy in danger and the window of opportunity for addressing the crisis "is small and fast closing," said Filippo Grandi, the deputy head of U.N. Relief and Works Agency, the international body responsible for Palestinian refugees.

"Gaza risks becoming a virtually 100 percent aid-dependent, closed-down and isolated community within a matter of months or weeks, if the present regime of closure continues," Grandi said at a news conference.

He appealed to "the Palestinian Authority, Israel and all other parties" to open the crossings, saying failure to do so would lead to "disastrous consequences, an atmosphere of hopelessness and despair in which extremism likely to take hold."

Even before Hamas' takeover, 1.1 million Gazans received foreign food assistance, a figure that rose sharply as a result of Israeli trade restrictions and an international aid embargo imposed after Hamas won 2006 elections.

Separately, the Association of Palestinian Businessmen reported that cumulative losses to industry in Gaza had reached $23 million since the Hamas takeover. If the closure continues, at least 120,000 could lose their jobs, the association predicted.

Two weeks ago, the Palestinian Federation of Industries reported that the closure of Gaza had forced the dismissal of about 70,000 of 120,000 private sector workers, driving unemployment above 40 percent.

The Hamas takeover has left Gaza isolated, but has also had the effect of jump-starting peace moves. Israel and the international community are scrambling to shore up President Mahmoud Abbas of the rival Fatah movement, who formed a moderate government that rules the West Bank.