Terrorist attacks result in the deaths of more than 20,000 people every year. Terrorist groups, which are rarely random or senseless in their actions, tend to use strategic weapons that cause more casualties and increase their notoriety. Although terrorist organizations use various types of weapons, they often prefer improvised explosive devices (IEDs) due to their accessibility and ease of creation. IEDs can be strategically placed or affixed to targeted equipment with minimal effort.
An IED is a homemade explosive device designed to inflict damage, cause disruption, or instill fear. These devices are employed by a variety of actors, including criminals, terrorists, insurgents, vandals, and suicide bombers. The design and potential impact of IEDs can vary significantly, ranging from simple pipe bombs to more sophisticated devices capable of causing extensive damage and loss of life. IEDs can be deployed in several ways, including being carried by an individual, planted in a vehicle, sent via a package, or concealed along roadways. The term “IED,” commonly referred to as roadside bombs, became widely recognized during the Iraq War, which began in 2003.
Some examples of improvised explosive devices (IEDs) include truck bombs, pipe bombs, and devices triggered by cell phone timers. On April 19, 1995, a truck bomb, made from ammonium nitrate fertilizer and nitromethane, exploded outside the Alfred P. Murrah Federal Building in Oklahoma City, killing 169 people. In the 1996 Olympics in Atlanta, a pipe bomb filled with nails exploded in Centennial Olympic Park, killing two and injuring several others. On March 11, 2004, in Madrid, 10 explosions rocked four commuter trains, killing 191 people and injuring over 1,800. The bombs were made from Goma-2 ECO explosives and metal fragments, initiated by cell phones. On July 7, 2005, four suicide bombers carried out attacks on London’s transportation system, killing 52 and injuring hundreds. The explosives were believed to be TATP, based on evidence found in an arrested suspect’s apartment.
The procurement of arms and explosives by terrorist groups for deploying IEDs is influenced by several critical factors. First, state sponsorship of terrorism is a significant factor, as political interests and definitional ambiguities lead to varying approaches to addressing terrorism. Non-state actors perceived as allies often receive support, while those labeled as terrorists are targeted. For instance, Iran-backed militia groups in the Middle East receive logistical assistance from Tehran, including rockets, mortars, missiles, and materials used to construct IEDs. Global Terrorism Trends and Analysis Center (GTTAC) reports the use of IEDs in 134 attacks by such groups between 2018 and 2024. Another critical factor is the occurrence of proxy wars, in which non-state actors are provided with weapons and financial support by various states, despite the violent nature of their actions. In Syria, GTTAC recorded 88 terrorist perpetrators from 2018 to 2024, supported by Russia, the Gulf States, Turkiye, and Iran. Porous borders in regions with active terror groups, such as Boko Haram in Nigeria, Al Shabaab in Somalia, and ISIS in Syria, facilitate the smuggling and transfer of arms and explosives. Additionally, endemic corruption in countries plagued by terrorism is closely linked to weak governance, with high terrorism levels correlating with poor rankings on the Corruption Perception Index. The convergence of criminal and terrorist organizations further exacerbates this issue, as these groups collaborate to achieve mutual interests and gain access to weaponry and explosives. Lastly, the financial capacity of terrorist groups, often sustained through illicit trafficking and smuggling activities, enables them to procure the necessary resources to manufacture and deploy IEDs.
According to data from the GTTAC, firearms were the most commonly used weapon by terrorist groups, accounting for 25,570 incidents, or 50.2% of all terrorist attacks between 2018 and 2023. Improvised explosive devices (IEDs) were the second most prevalent, with 8,210 incidents (15.93%), followed by explosives in 7,781 attacks (15.1%), incendiary devices in 1,831 attacks (3.55%), and melee weapons in 1,213 attacks (2.29%) during the same period.
The number of terrorist incidents between 2018 and 2024 fluctuated between 8,000 and 10,000, as seen in Figure 1 below. Despite these variations in the overall number of incidents, the frequency of IED-related attacks exhibited a gradual decline over the same period. The proportion of IED-related incidents ranged from 10% to 22%, with the lowest recorded percentage in 2024, at 10.91%. A significant contributing factor to the low proportion in 2024 is the increase in missile attacks by Hezbollah, as documented by GTTAC, which recorded over 1,400 such attacks in Israel in 2024.
The GTTAC data from 2018 to 2024, as seen in Figure 2 below, highlights trends in the use of IEDs in terrorist attacks. Total fatalities decreased steadily from 32,864 in 2018 to 18,987 in 2024. However, fatalities caused by IEDs saw notable fluctuations. In 2019, there was a sharp increase in IED-related fatalities, with 5,203 deaths, making up 19.8% of all fatalities. Following this peak, the number of IED-related fatalities gradually decreased over the next several years. By 2024, fatalities due to IEDs dropped to 1,985, or 10.4% of the total. Despite the overall decline in total fatalities, IEDs continued to be a significant tool in terrorist attacks throughout the period. The proportion of IED-related fatalities fluctuated, with a noticeable dip in 2023, when only 1,777 fatalities (8.2%) were attributed to IEDs. This suggests that while the total number of fatalities and IED-related deaths has generally decreased, IEDs remain an important weapon for terrorist groups.
The GTTAC data on the number of victims targeted and killed in IED attacks, as seen in Figure 3 below, highlights the varying levels of vulnerability among different groups. The general population suffered the highest number of casualties, with 2,324 victims. Military personnel were also significantly targeted, accounting for 1,720 fatalities, which reflects the high targeting of military forces in such attacks. Government personnel faced substantial casualties as well, with 1,321 fatalities, indicating that state institutions are frequently targeted by terrorist groups. Political figures, however, were the least affected, with only 28 fatalities, possibly due to their relatively lower visibility or priority in these attacks. Additionally, groups and professionals each saw a moderate number of fatalities, with 349 and 182 victims, respectively, suggesting that specific sectors or individuals are targeted for their symbolic or strategic value.
The GTTAC data on IED attacks by terrorist typologies, as seen in Figure 4, indicates the varying use of IEDs across different ideological groups. Religious (jihadist) groups accounted for the largest share of IED attacks, with 2,703 incidents, followed by separatist groups with 1,973 attacks. Left-wing groups were responsible for 810 IED-related incidents. Interestingly, far-right groups are notably absent from this data, as they have never been reported to use IEDs, reflecting a distinct operational preference for other methods of violence. Anarchist and vigilante groups contributed only a small number of incidents, with 11 and 7 IED attacks, respectively.
The data presented in Figure 5 offers a group-level analysis of IED usage from 2018 to 2024, focusing on several of the top 10 perpetrators responsible for the most attacks in 2024, namely Al-Shabaab, ISIS-Core, JNIM, and Hezbollah. Al-Shabaab maintained a relatively high level of IED activity throughout the period, with 138 attacks in 2018, fluctuating numbers in subsequent years, and a peak of 170 attacks in 2019. However, a steady decline in their use of IEDs was observed in the following years. The Al-Qaeda-affiliated group utilized IEDs in 60 of its 261 attacks in 2024. ISIS-Core exhibited considerable fluctuations in IED use, reaching a peak of 246 attacks in 2019 before gradually decreasing to 55 out of 560 attacks in 2024. This trend may indicate a reduction in ISIS’s territorial control and a strategic shift towards leveraging sleeper cells for low-profile shooting attacks in Iraq and Syria, in response to significant weakening by international counterterrorism operations in recent years.
Jamaat al-Nusra wal-Muslimin (JNIM), an al-Qaeda-affiliated group operating in the Sahel region, exhibited relatively stable IED activity, with a peak of 71 attacks in 2022, followed by moderate levels in subsequent years, including 37 out of its 377 attacks in 2024. JNIM’s sustained reliance on IEDs underscores the continued strategic importance of these devices in its operational activities across the Sahel. Conversely, Hezbollah, which had minimal recorded IED activity in earlier years, experienced a significant increase in 2024, with 97 incidents out of its 1,450 attacks in 2024. This notable escalation is likely attributable to the group’s expanding involvement in the Middle East, particularly in the aftermath of the October 7 terror attacks, which exacerbated regional tensions.
In conclusion, the data provides valuable insights into the changing landscape of IED-related terrorism. The steady decline in the proportion of IED incidents, particularly in 2024, is partly due to intensified military actions targeting terrorist groups in rural areas. This pressure has forced these groups to adapt, shifting towards direct assault methods, such as storming and shooting attacks. Jihadist organizations remain the primary perpetrators of IED-related terrorism. However, despite the overall decline in IED use, groups like ISIS and Al-Qaeda continue to rely on these tactics in their areas of operation. The decrease in IED usage may also be linked to a broader shift in terrorist weaponry, with a notable rise in the use of missiles and drones. Various groups, including Iran-backed militias and Al-Qaeda affiliates in regions like Syria, Yemen, and the Sahel, have increasingly turned to drones. This strategy offers lower risk to the attackers while potentially causing greater harm and attracting more attention.
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