Israel has frozen the shipment of building materials into Gaza after discovering what it says is a sophisticated "terror tunnel" into its own territory from Palestinian land.
"Due to security reasons, [the army] decided to stop for now the transfer of building materials into Gaza," Guy Inbar, a spokesman for the Israeli defence ministry unit responsible for civilian affairs in the Palestinian territories, told the AFP news agency on Sunday.
Inbar did not say how long the ban would remain in force.
Last month, Israel permitted cement and steel deliveries into the Gaza Strip - under Israeli blockade for six years - for use by the private sector for the first time since 2007.
It had banned such transfers for fear that the Palestinian movement Hamas, which rules Gaza, would use them to fortify its positions and build tunnels for attacks on Israel.
The Israeli army said the tunnel was buried 18m underground, made of concrete and ran for 1.7km with 450m extending into Israel.
It had lighting and a rail for a small trolley, "probably intended to transfer terrorists or soldiers from side to side rapidly", it added.
The Israeli defence minister, Moshe Yaalon, said in a statement that the discovery of the tunnel "prevented attempts to attack Israeli civilians and soldiers".
He said it was "further proof" that Hamas "was continuing to prepare itself for confrontation with Israel and terror activities".
Israel and Hamas reached a truce, brokered by Egypt, after a deadly confrontation last November.
Its statement made mention of Israeli soldier Gilad Shalit, who was abducted by Palestinian fighters and transferred to Gaza via a tunnel in 2006 and held for five years.
The army said work on the tunnel probably lasted over a year.
Israeli NGO Gisha, which lobbies for freedom of movement for Palestinians, urged Israel to lift the building material freeze, saying it would affect civilians and humanitarian projects in blockaded Gaza.
"It is not clear how blocking the entrance of construction materials, including those intended for international projects, promotes that goal."