Israeli defense officials on Thursday said the government has begun work on a massive underground barrier along the border with Gaza meant to block Hamas militants from tunneling into Israel. The project is the hallmark of a huge Israeli effort to halt the Hamas tunnels, which military officials have identified as a strategic threat. Hamas militants have used underground tunnels to attack Israelis.

During a 2014 war, Hamas militants managed on several occasions to make their way into Israel through their tunnel network, though they did not reach nearby civilian areas.

Israel destroyed some 32 tunnels during that conflict and has announced the discovery of several more tunnels since then. Israel has already surrounded Gaza with a sophisticated above-ground fence fortified with sensors, cameras, barbed wire and watch towers.

The defense officials, speaking on condition of anonymity because they were discussing a classified matter, said work on the underground barrier had begun in recent weeks. When it is completed, it is expected to stretch the entire length of the roughly 70-kilometer border. The officials said the concrete barrier will run dozens of meters deep. Israel is currently building an initial phase of the barrier over a small stretch of land measuring dozens of meters.

At Kibbutz Erez, a community on Israel's southern border with Gaza, work crews were busy Thursday using cranes, heavy machinery and cement mixers. Caravans were scattered around the site, while large metal pipes ran along the ground. The officials said the barrier's construction could take years.

Salah Bardawil, a senior Hamas official in Gaza, said the group would not be deterred. "The Palestinian people and the resistance can overcome all the obstacles made by the occupation. The resistance is creative and advanced and doesn't care about the occupation's procedures," he said.

Meanwhile, the Palestinian high court on Thursday postponed municipal elections that had been set for next month, putting on hold what would have been the first real test of political support for archrivals Hamas and Fatah in a decade. The delay of the vote is bound to stir more tensions between Fatah, the movement of Western-backed Palestinian President Mahmoud Abbas, and Hamas, an Islamic militant group.

It will also make it less likely the two sides will be able to end their territorial split, with Hamas entrenched in the Gaza Strip and Abbas in autonomous enclaves of the Israeli-occupied West Bank. The rift has undercut Abbas' claim to be a leader of all Palestinians and weakened him in past negotiations with Israel on Palestinian statehood.

The Oct. 8 vote would have been their first electoral contest since Hamas drove Abbas loyalists from their posts in Gaza in 2007, a year after the group won parliament elections. Since the Hamas takeover, repeated reconciliation attempts have failed while both sides deepened control over their respective territories.