A/HRC/34/64 supporting strike operations in Aleppo governorate were in Aleppo, Homs and Latakia. On 23 September, for example, Russian aircraft conducted 42 air sorties, making at least 28 confirmed air strikes in eastern Aleppo city. 15. The use of air-delivered cluster munitions increased during the period under review. Cluster munitions disperse smaller submunitions, which kill and injure over a wide area. In the case of some of the munitions observed, each cluster bomb dispersed more than 500 submunitions. As a result, Aleppo is now contaminated with significant quantities of unexploded ordnance. 16. Victims and witnesses frequently reported aerial attacks with “bunker-buster” bombs, known technically as concrete-piercing munitions. Only small numbers of these bombs were employed. Other highly explosive weapons used, particularly those with delay fuses, generated similar effects and could be easily mistaken for bunker-buster bombs by the layperson. 17. Throughout 2016, Syrian air forces launched air strikes using chlorine bombs in eastern Aleppo city. There is no information to support the claim that the Russian military ever used any chemical weapons in the Syrian Arab Republic. While civilians exposed to chlorine may exhibit symptoms similar to those exposed to vesicants, such as sulphur mustard, chlorine gas was identified as the most likely agent in several cases. 18. Both the Syrian forces and armed groups used improvised and craft-produced weapons. Improvised weapons, such as air-delivered munitions (including barrel bombs), rocket-assisted munitions and mortars, are relatively inaccurate and imprecise, and are often highly explosive. Large improvised air-delivered munitions were employed solely by the Syrian air force. Improvised rocket-assisted munitions and mortars were primarily employed by armed groups. The use of both resulted in extensive civilian casualties. 19. Armed groups, which were not in control of the skies, used an array of improvised mortars. Many of these, including a common spigot mortar widely referred to as Jahannam or the “hell” cannon, employ cooking gas pressure vessels as projectiles. Broadly speaking, these mixtures are capable of producing blasts equivalent to 22 to 33 kilograms of TNT. A typical example may produce a fatal blast pressure up to 15 metres from the site of detonation, and injurious blast effects extending up to 40 metres. Most projectiles from these weapons travel 400 to 600 metres. 20. Armed groups also frequently employed indirect fire, 2 primarily by artillery systems. In numerous cases, these weapons were used to attack targets located amid concentrations of civilians, amounting to indiscriminate attacks. In other cases, armed groups intentionally applied indirect fire against enemy-held territory without targeting specific military objectives. The use by Syrian forces and armed groups of guided munitions in Aleppo appears to have been limited to anti-tank guided missiles to attack buildings and vehicles. V. Eastern Aleppo city A. Establishment of a siege 21. Once the country’s economic capital and most-populated city, Aleppo remained of major strategic importance to all parties. In 2012, the city was effectively divided in two 2 6 Direct fire relies on a direct line of sight to the target, while indirect fire does not. To be accurate, indirect fire should employ an observer to correct fires.