The agreement on monitoring the supply of materials "must get up and running without delay," said Robert Serry, the UN envoy for the Middle East.
The deal, announced by Serry at a UN Security Council meeting, would allow private companies to move in to rebuild Gaza after a recent 50-day war ravaged the enclave and left more than 2,140 Palestinians dead.
It addresses Israel's concerns that cement and other materials could be used to rebuild Hamas tunnels by setting up a UN monitoring mechanism of the imports.
He appealed for the re-opening of crossing points to allow the delivery of materials and emphasised that quick action on reconstruction would provide a "signal of hope to the people of Gaza."
Egypt is due to host a donor conference for Gaza reconstruction on October 12, supported by Norway.
"The crisis in Gaza is far from over and the window of opportunity to address critical needs and stabilise the situation is short," Serry warned.
Following weeks of Egyptian-brokered negotiations, Israel and Hamas agreed to halt their fire in Gaza on August 26 after 50 days, their deadliest confrontation in years.
The indirect talks are set to resume mid-September to discuss longer-term issues.
UN diplomats, however, are concerned about Israeli and Palestinian commitment to peace talks, with one Security Council member saying that the sides appeared to be drifting toward a "cold peace."