Bomb the Area, Gas the Tunnels:
Israel’s Unbridled War on Gaza’s Underground
Yuval Abraham / +972 Magazine
Unable to pinpoint Hamas commanders in Gaza’s tunnels, the Israeli army decimated entire residential blocks with bunker-buster bombs to crush the passages below and flood them with lethal fumes
(February 6, 2025) — The Israeli army intensively bombarded residential areas in Gaza when it lacked intelligence on the exact location of Hamas commanders hiding underground, and intentionally weaponized toxic byproducts of bombs to suffocate militants in their tunnels, an investigation by +972 Magazine and Local Call can reveal.
The investigation, based on conversations with 15 Israeli Military Intelligence and Shin Bet officers who have been involved in tunnel-targeting operations since October 7, exposes how this strategy aimed to compensate for the army’s inability to pinpoint targets in Hamas’ subterranean tunnel network. When targeting senior commanders in the group, the Israeli military authorized the killing of “triple-digit numbers” of Palestinian civilians as “collateral damage,” and maintained close real-time coordination with U.S. officials regarding the expected casualty figures.
Some of these strikes, which were the deadliest in the war and often used American bombs, are known to have killed Israeli hostages despite concerns raised ahead of time by military officers. Moreover, the lack of precise intelligence meant that in at least three major strikes, the army dropped several 2,000-pound bunker-buster bombs that killed scores of civilians — part of a strategy known as “tiling” — without succeeding in killing the intended target.
“Pinpointing a target inside a tunnel is hard, so you attack a [wide] radius,” a Military Intelligence source told +972 and Local Call. Given that the army would have only a vague approximation of the target’s location, the source explained, this radius would be as large as “tens and sometimes hundreds of meters,” meaning these bombing operations collapsed multiple apartment buildings on their occupants without warning. “Suddenly you see how someone in the IDF really behaves when given the opportunity to wipe out an entire residential block — and they do it,” the source added.
The investigation also reveals how Israel has known for years that the use of bunker-buster bombs releases the lethal gas carbon monoxide as a byproduct, which can kill people inside a tunnel through asphyxiation even at a distance of hundreds of meters from the strike location. After discovering this by chance in 2017, the army first tested it as a strategy in Gaza in 2021, and employed it in its efforts to kill Hamas commanders after October 7. This way, the army could attack targets without knowing their precise location, and without having to rely on direct hits.
“The gas stays underground, and people suffocate,” Brig. Gen. (res.) Guy Hazoot, the only source willing to be named, told +972 and Local Call. “[We realized] we could effectively target anyone underground using the Air Force’s bunker-buster bombs, which, even if they don’t destroy the tunnel, release gases that kill anyone inside. The tunnel then becomes a death trap.”
In January 2024, a spokesperson for the Israeli army told +972 and Local Call in response to a previous investigation that it “has never used and does not currently use byproducts of bomb deployment to harm its targets, and there is no such ‘technique’ in the IDF.” Yet our new investigation reveals that the Air Force conducted physio-chemical research on the effect of the gas in enclosed spaces, and the military has deliberated over the method’s ethical implications.
Three Israeli hostages — Nik Beizer, Ron Sherman, and Elia Toledano — were definitively killed by asphyxiation as a result of a Nov. 10, 2023, bombing that targeted Ahmed Ghandour, a Hamas brigade commander in northern Gaza. The army told their families that, at the time of the bombing, it was unaware that hostages were being held near Ghandour. However, three sources with knowledge of the strike, which was led by the Shin Bet, told +972 and Local Call there was “ambiguous” intelligence indicating that hostages might be in the vicinity, yet the attack was still authorized.
According to six sources, this was not an isolated case but one of “dozens” of Israeli airstrikes that likely endangered or killed hostages. They described how the military command greenlighted attacks on the homes of suspected kidnappers and the tunnels from which senior Hamas figures were directing the fighting.
While attacks were aborted when there was specific, definitive intelligence indicating the presence of a hostage, the army routinely authorized strikes when the intelligence picture was murky and there was a “general” likelihood that hostages were present in the vicinity of a target. “Mistakes definitely happened, and we bombed hostages,” one intelligence source said.
Israel’s efforts to maximize the chances of killing senior militants hiding underground also included attempts to crush parts of a tunnel network and trap the targets inside. Sources described incidents where vehicles fleeing an attack site were bombed without specific intelligence about who was inside, based on the assumption that a senior Hamas figure might be trying to escape.
“The entire region felt and heard the explosions,” Abdel Hadi Okal, a Palestinian journalist from Jabalia who witnessed several major Israeli bombing operations — which Palestinians often refer to as “fire belts” — during the early weeks of the war, told +972 and Local Call. “Entire residential blocks were targeted with heavy missiles, causing buildings to collapse and fall on top of each other. Ambulances and Civil Defense vehicles were unable to contend with the scale of the bombardment, so people had to use their hands and some light equipment to pull bodies from under the rubble of houses. There was no possibility for anyone to survive.”
Part 1: The Gas Effect
A Surprise Discovery
The gas effect was discovered unintentionally in October 2017. At the time, Brig. Gen. (res.) Guy Hazoot led a division in the Southern Command. He recounted the sequence of events to +972 and Local Call, corroborated by three other military sources.
According to Hazoot, the then-IDF Chief of Staff Gadi Eizenkot was abroad and had tasked his deputy, Aviv Kochavi, with addressing a pressing issue: Palestinian Islamic Jihad (PIJ) had dug a tunnel underneath the fence that encages the Gaza Strip, reaching about two kilometers from Kibbutz Kissufim. Kochavi ordered the Air Force to bomb the tunnel with a bunker-buster bomb but instructed them to avoid killing more than five PIJ operatives to prevent unnecessary escalation in Gaza.
Then, something unexpected happened. “Even though we fired the bombs on [the Israeli side] of the border, everyone in the tunnel [inside Gaza] died,” Hazoot explained. “Another 12 PIJ rescue personnel entered after the explosion and also died from suffocation. Even those with masks died.” This was the “breakthrough moment,” Hazoot said, when it became clear that bunker-buster bombs detonated in tunnels dispersed carbon monoxide gas as a byproduct, which remained in the tunnel for days.
Carbon monoxide, known as the “silent killer,” is colorless, odorless, and tasteless, and is particularly lethal to humans. Annually, approximately 30,000 people die from inhaling it due to faulty heaters, engines, and furnaces in enclosed spaces with low oxygen levels.
The Air Force subsequently conducted a physio-chemical study on the effect of the gas in confined spaces, which found that it was difficult to predict the precise radius of its lethal spread. “There are probabilities,” a source in the Air Force explained to +972 and Local Call. “It’s not binary, where everyone within this radius dies and beyond it no one does. There’s a radius of high probability, medium probability, and low probability of dying from the gas.”
Security sources noted that using bunker-buster bombs that release gas underground as a byproduct overcame the challenge of having to pinpoint a target’s exact location inside a tunnel. But it also presented a dilemma.
“It was made clear to us how sensitive this issue is, the very fact that this effect exists,” the Air Force source said. A source who participated in a discussion about the use of the technique in 2021, led by the then-chief of the army’s Southern Command, Eliezer Toledano, explained: “Everyone took it very seriously in the discussion, the fact that gas is what kills. They feared it would cause significant damage to [Israel’s] image.”
Military officials emphasized to +972 and Local Call that the intent was to use the chemical byproduct solely to kill Hamas operatives “who intended to fight the IDF.” Hazoot, along with other security sources, also stressed that the bombs themselves are “conventional weapons,” as the gases are a byproduct of standard bombs, not chemical or biological warheads. “The gases have nowhere to escape,” Hazoot said. “They stay underground, and people suffocate. It’s a conventional weapon, only its effect underground is different. The bombs become more lethal.”
However, Michael Sfard, an Israeli human rights lawyer and expert in international law, told +972 and Local Call: “Even if the bombs releasing the gas are conventional and the gas is only a byproduct, the deliberate use of this ‘side effect’ as a method of warfare violates prohibitions outlined in the laws of armed conflict. The use of toxic or asphyxiating gas in combat contravenes the provisions of the Chemical Weapons Convention and longstanding international declarations predating it, and is classified under the Rome Statute of the International Criminal Court as a war crime.”
Sarah Harrison, a senior analyst at the International Crisis Group and a former Pentagon lawyer who advised U.S. armed forces, affirmed that the intentional use of carbon monoxide as a weapon is illegal under customary international law. While bunker-buster bombs are not outlawed per se, “if the intent is to only use the conventional weapon as a device to transport what is otherwise a chemical weapon, then that would be, in my opinion, an illegal use,” she told +972 and Local Call. “There are lots of lawful weapons you can use unlawfully.”
In response to our inquiry, a spokesperson for the Israeli army again denied that it uses this technique to kill Hamas leaders, calling the allegation “baseless.”
Creating Death Traps
Hazoot and other sources revealed that Israel’s first attempt to employ bunker-buster bombs to cause mass fatalities among militants through gas-induced asphyxiation was in “Operation Lightning Strike,” the massive bombing of Hamas’ tunnel network during the broader “Operation Guardian of the Walls” in May 2021.
Ahead of that operation, a source from the Israeli Air Force explained, professional ranks in the Air Force raised concerns that the extensive use of bunker-buster bombs to detonate underground could cause entire buildings above ground to collapse, endangering large numbers of civilians. “There was an effort to convey to the command level that this operation was risky, that buildings might collapse, and that we didn’t fully understand what might happen,” the source said. “But they went ahead with it anyway.”
These predictions materialized during the operation on May 16, 2021. The attack on Hamas’ tunnel network in the Rimal neighborhood of Gaza City collapsed several residential buildings, killing 44 civilians.
Hazoot explained that during “Guardian of the Walls,” the army aimed to mislead Hamas into believing that Israeli troops were about to invade Gaza, prompting its operatives to retreat into the tunnels. In the attack to follow, he told the Israeli newspaper Israel Hayom in an interview last year, the army expected to kill “between 500 and 800 operatives” through asphyxiation upon dropping “460 bunker-buster bombs on them simultaneously.”
The deception failed: Hamas operatives did not enter the tunnels. Yet the bombardment proceeded regardless.
The sources stated that these attacks shocked some within the Air Force and Southern Command, as they felt the actions lacked military logic once it became evident that Hamas operatives were not retreating to the tunnels — foreshadowing some of the army’s modes of operationsince October 7. ‘
“At a certain point, [the army] realized Hamas had figured out the strategy. And they said, ‘Well, let’s just blow everything up and create destruction,’” a military source claimed. “There was no rational decision-making. It didn’t feel like there was a purpose. It felt like an attempt to display power.”
According to Hazoot, Hamas soon caught on. “Hamas learned lessons from ‘Guardian of the Walls,’” he explained. “They purchased 1,300 blast doors and distributed them throughout the tunnels. They created multiple ventilation shafts to disperse the gases and also implemented new tunnel-digging techniques involving twists and turns” — techniques which, according to Hazoot, helped to trap gas and prevent it from spreading further.
Indeed, a Hamas spokesperson confirmed to +972 and Local Call: “Al-Qassam Brigades took measures to protect its elements in the tunnels from the gases that the Israeli army was sending during its strikes.”
An intelligence source involved in Israeli military activity in both Gaza and Lebanon told +972 and Local Call that the understanding within the security establishment is that Hezbollah Secretary General Hassan Nasrallah likely also died from asphyxiation — though in Lebanon gas was not weaponized as a deliberate assassination method, as it was in Gaza.
“With Nasrallah, dozens of bombs were dropped, and the IDF hoped one of them would detonate and directly kill him in the bunker,” the source said. “In Gaza, on the other hand, when attacking a tunnel, you don’t know exactly where the senior figure is located. So you attack several areas of the tunnel, creating the potential that he will die from asphyxiation.”
The army’s deliberate use of gas-induced asphyxiation as an assassination technique in Gaza was also highlighted by Nir Dvori, a military analyst for Israel’s Channel 12, in his account of the bombing that killed senior Hamas militant Marwan Issa in Nuseirat refugee camp in March 2024.
“The Air Force used bunker-buster bombs and especially heavy explosives to strike the underground compound,” Dvori wrote, citing military sources. “The reason for the heavy bombardment and secondary explosions was to ensure that anyone not killed by the blast itself or the tunnel collapse would die from asphyxiation or inhalation of hazardous substances.”
Continue reading online:
Part 2: Endangering Hostages
Part 3: ‘Tiling’ Neighborhoods
This article has been updated to include responses to +972 and Local Call’s inquiries from Hazem Qassem, a Hamas spokesperson in the Gaza Strip, that were received after publication.
Posted in accordance with Title 17, Section 107, US Code, for noncommercial, educational purposes.
