Lush trees drip with fruit in a clementine orchard near a lookout point at the Nir Am kibbutz. Hashem Barawi, a Palestinian worker from Gaza, hands the kibbutz’s agricultural head Ofer Lieberman several of the sweet citrus fruit. This idyllic setting, home to 400 Jewish Israelis, is one of the closest communities along Israel’s border with northern Gaza. “It’s quiet here. It’s like heaven,” says Lieberman.

Barawi and Lieberman have been friends and colleagues for 35 years. They remember when Gaza was open and they could travel to visit each other, though now only Barawi is allowed to travel into Israel, and only with difficulty. Yet the two men should be enemies, at least judging by the relations between their respective leaderships — the Israeli government and Hamas, the Islamic militant group that has ruled Gaza since it won an election in 2005 and seized control of the Gaza Strip from Palestinian Authority forces in 2007. Increasingly bellicose rhetoric has put Hamas and the Israeli leadership on a collision course toward war, barely a year and a half after the last open conflict in 2014, which began with rocket fire and left 2,100 Palestinians and 70 Israelis dead.

But the next war will likely be waged underground. Hamas have announced they are building tunnels into Israel, and residents of the kibbutz Nir Am and other communities along the border have recorded sounds of tunnel diggers working underneath their homes. And the thought of militants operating beneath their feet has Israelis — not unaccustomed to terror — increasingly fearful. “Personally I prefer missiles — because you can get inside a shelter and it’s O.K., but once a terrorist is inside the kibbutz with a gun, I don’t know what would happen,” says Lieberman. “I really hope it will not happen, but we just don’t know.

Tunnels are not a new threat. The Israeli soldier Gilad Shalit was kidnapped by a militant who entered Israel using a tunnel in 2006. He was held for five years and freed only when Israel released 1,027 prisoners. At the height of the last war, the underground threat became real when 10 Hamas militants emerged from a tunnel in a wheat field on the periphery of Nir Am. They were disguised in Israeli army uniforms. Four Israeli soldiers were killed, and all 10 of the militants, in an exchange of fire.

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That atmosphere of vulnerability intensified this year after a Jan. 29 funeral of seven diggers who were killed when winter rains allegedly caused five tunnels to collapse. “East of Gaza City, heroes are digging through rock and building tunnels, and to the west they are experimenting with rockets every day,” Hamas leader Ismail Haniyeh said at the funeral. While Hamas blamed their deaths on the heavy rain, when the Palestinian news agency Maan asked the Israeli army’s Coordination of the Government Activities in the Territories unit chief, General Yoav Mordecai, if Israel had a hand in the collapse of tunnels, he replied, “God knows.”

Hamas started digging tunnels immediately after the war ended in 2014 and says it has constructed more than 50 in that time. While Israel acknowledges that there are tunnels, it says these numbers are inflated. For Hamas, the purpose of these tunnels is simple: either to kidnap Israeli civilians in order to use them as leverage for the release of more Palestinian prisoners, or to attack Israelis and kill them.

In 2014 the Israeli army discovered 32 tunnels, half of which penetrated into Israel. The army believes it took Hamas four years to build these 32 tunnels, which were all destroyed in the last war. But in some cases Israel was only able to blow up the entry or exit points of the tunnels, or collapse them in the middle. Israel is working desperately to develop technology along the border to try to halt further construction, but it has refused to divulge details on just how that might work — or how effective it will be.

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“It’s a kind of race between us and them. We will find a solution, and they will then find several answers,” says Atai Shelach, a former commander of Israel’s military combat engineering unit, who now heads a company providing engineering products. “This challenge won’t vanish in the next three to four decades. It’s not just a race, it’s a marathon race; we have to be patient.”

Heavy machinery and engineering equipment were lined up along Israel’s border with Gaza when TIME visited recently. While the Israeli army won’t confirm what is being done with the equipment, military spokesman Peter Lerner confirmed that army has 100 engineering devices “carrying out various activities along the border to reveal and expose tunnels.”

These devices have been rumored to be part of a secret underground defense system, similar to Israel’s Iron Dome missile defense system, which detects and intercepts rockets being fired from Gaza. According to a recent report in the Financial Times, Israel secured $120 million in U.S. funding this year to develop technology to detect and destroy tunnels. On Feb. 20, during Friday prayer, Haniyeh of Hamas announced that al-Qassam, the group’s military wing, had discovered Israeli electronic equipment meant to find underground tunnels. He said the equipment included cameras and sensors.

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But while Israel forges ahead with its high-tech detection system, Hamas says it has workers constructing tunnels up to 24 hours a day. “The death of the tunnel workers during the last severe storm gave a very serious signal that Hamas is working around the clock, even in the worst weather circumstances,” says Mkhaimer Abusada, a professor of political science at al-Azhar University in Gaza.

While Abusada estimates that two-thirds of the Gazan population do not support another war with Israel, there are many who do. “The Palestinian community in Gaza is divided — those affiliated with Hamas are very comfortable with the strategy of digging tunnels and developing missiles. Hamas create an illusion that Israel will be defeated and that people will be able to pray in al-Aqsa mosque — people buy this fantasy.”

Yousra al Shobaki, mother of 22-year-old Ghazwan, who dug tunnels and fought for Hama’s military wing, al-Qassam, told TIME she supports Hamas’ efforts. “We will win in the end. I ask all the mothers in Gaza to support the jihad and to go to the mosques to teach them how to defend their country — and to teach their sons what jihad means. I wish all the young Qassam men the best in their work, and I hope they will win in the end of all these conflicts with the Israelis. There is no such thing as Israel — these people occupied our land, there is nothing called Israel.”

The situation for everyday Palestinians in Gaza has become dire — 900,000 of the 1.2 million–strong population are in need of aid support in the aftermath of the last war. Earlier this month, the U.N. Office for the Coordination of Humanitarian Affairs in the Occupied Palestinian Territories announced the need to collect $571 million for emergency services across the Palestinian territories, most of which would go to Gaza. With only a quarter of the 18,000 homes destroyed during the war in any state of repair, much of Gaza is still in rubble, with thousands of people remaining homeless. Dr. Abusada believes that some of the much needed building materials entering to Gaza through Israel were ending up in Hamas’ hands, where they were redirected toward tunnel construction.

Back in kibbutz Nir Am, Barawi and Lieberman agree that a war would be catastrophic — and so it would be for ordinary Palestinians and Israelis alike. But the decision may not be up to them.

— Additional reporting by Mohamed al-Zaharna

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