Shira Rubin

Special for USA TODAY

KIBBUTZ NIR AM, Israel — The last Gaza war began in the air with rockets that Hamas militants fired at Israel. Now, Israelis living next door to the Palestinian territory see worrisome signs that the next war will be waged underground.

They live above ground zero: Hamas appears to be building new tunnels under their feet to smuggle fighters into Israel to kill or kidnap residents.

In response, the Israeli government is stepping up efforts — and developing secret high-tech methods — to detect and destroy the labyrinth of tunnels Hamas builds to circumvent a tight embargo that Israel and Egypt imposed around Gaza.

Israel is "concentrating considerable engineering and intelligence efforts to combat this threat," Israeli military chief Gadi Eizenkot said Tuesday in Herzliya. The army also notified Kibbutz Nir Am residents that soldiers are on alert in the case of a surprise tunnel attack.

Such assurances aren't calming the nerves of this community, located just over a mile from the Gaza border where several tunnels were discovered and destroyed during the 2014 war.

Extent of tunnels under Gaza takes Israel by surprise

“This conflict has reached a point where you’re fighting not another army, but terrorism, which ... makes all public spaces into a battlefield,” said Betty Gavri, an insurance agent who lives on the kibbutz.

Israel says Hamas has resumed digging tunnels since the last war ended. Hamas claims it has built more than 50 tunnels in the past 18 months, but Israel rejects that as an exaggeration. The Israeli army noted Hamas took more than four years to dig the 32 tunnels discovered in 2014.

A military assessment published Wednesday in the Yediot Ahronot newspaper said more than 1,000 Gazan diggers are progressing at roughly 160 feet per week on one long, high-quality tunnel. The tunnel is being constructed on top of smaller tunnel systems estimated to be 6 feet high, 5 feet wide and 80 feet deep, the report said.

After winter rains last month caused tunnels to collapse, killing at least 11 diggers, Hamas — a U.S.-designated terror group governing Gaza — boasted that it has greatly expanded its network of tunnels.

“East of Gaza City, heroes are digging through rock and building tunnels, and to the west they are experimenting with rockets every day,” Hamas political leader Ismael Hanieyeh said Jan. 29 at the funeral for seven of those killed.

Hamas' tunnels provide a rare advantage against a vastly superior Israeli military, which deployed its Iron Dome defense system to intercept most of the rockets fired in 2014 by the militants.

Some tunnels have electricity and telephone lines, but most are small and only require manpower and persistence, both of which are abundant in Gaza. And the tunnels have been virtually impossible to detect from afar by Israeli technology.

A long-awaited breakthrough may be near. The Defense Ministry this month received a $120 million grant from the United States to develop an underground defense system able to detect the digging of tunnels dozens of yards below ground, according to Israeli media. The Financial Times reported that two Israeli security companies are racing to complete the so-called underground Iron Dome.

Much like the original Iron Dome anti-missile system, an underground equivalent could represent a major military defeat for Hamas and a big psychological boost for Israelis.

Since its withdrawal from Gaza in 2005, Israel has destroyed Hamas tunnels only to see new ones built. The most notable incident occurred in 2006, when a team of Palestinian fighters exited a tunnel on the Gaza border, killed two soldiers and abducted a third, Gilad Shalit.

Shalit was held captive for five years before he was released in exchange for 1,027 Palestinian prisoners, including Yehiya Sanwar, who has become a dominant figure in Hamas’ tunnel building initiative.

"Israel's only short-term option is to go into Gaza to destroy the tunnels, as was done in the 2014 war, which was enormously costly in terms of casualties and also politically," said Eado Hecht, a military doctrine researcher who testified last year before a U.N. commission examining the Gaza war. "But that does not actually prevent the tunnels from being rebuilt."

Developing an effective underground Iron Dome will be a tough challenge, given the extent of tunnel-building, said Yiftah Shapir, a senior fellow at the Institute for National Security Studies in Tel Aviv.

Even if sensor technologies can hear digging, Shapir said, “the system may have more trouble actually finding existing tunnels that are already active, where people may pass through very quietly," as opposed to animals burrowing or "whatever is going on down there.”