JERUSALEM — Israel has started allowing long-banned building materials into the Gaza Strip, its first key concession to the Palestinian territory’s ruling Hamas movement under the cease-fire that ended eight days of fighting last month, the military said Monday.

The military says the shipments will continue so long as the border remains quiet. But a Hamas official said the amount sent so far is small, and Gaza economists say it would take years of round-the-clock shipments to make a dent in the gap left by five years of blockade.