KISSUFIM, Israel (AP) — The Israeli military says a secretive project to build an underground wall along the border with Gaza is proving to be a deterrent against militant attack tunnels from the Palestinian territory.

In a briefing to reporters at the border Thursday, the military says the wall extends hundreds of feet below ground and is studded with sensors. It's also topped by a 26-foot metal fence.

Military spokesman Col. Jonathan Conricus wouldn't disclose details about the barrier's tunnel detection capabilities but says it's effective.

Excavating machines, concrete mixers and hundreds of workers are toiling furiously to complete the barrier by mid-2019 at a cost of about $700 million.

During the most recent war between Israel and Hamas, militants caught Israel off guard by attacking through its underground tunnel network.