Human Rights Watch reported Friday that the Saudi Arabia-led coalition, which is backed by the United States, fired Brazilian-made cluster bombs on civilians in the al-Dhubat neighborhood in Saada’s Old City, killing at least two people. The munitions were dropped “near two schools,” the organization says, noting that the attack also left at least eight people wounded, including one child.

This is not the first time cluster bombs have been used to kill civilians in the brutal, ongoing military assault that has now passed the 20-month mark. Human rights groups say that cluster munitions produced in the United States, United Kingdom and Brazil have been dropped on roughly a quarter of Yemen’s 21.

While 98 countries have ratified the 2008 Convention on Cluster Munitions, which bars the weapons, none of the countries that comprise the Saudi-led coalition have, and neither has Yemen. Notably, the bombing documented in the latest Human Rights Watch report took place on December 6, a day after Saudi Arabia, Brazil and the United States abstained from United Nations General Assembly endorsement of the international ban on the use of cluster bombs.

The countries abstained despite mounting concerns about use of the weapons, which leave a broad path of destruction, putting civilians at direct risk. “Cluster munitions are unacceptable for two reasons,” the Convention on Cluster Munitions states. “Firstly, they have wide area effects and are unable to distinguish between civilians and combatants. “Secondly, the use of cluster munitions leave behind large numbers of dangerous unexploded ordnance. Such remnants kill and injure civilians, obstruct economic and social development, and have other severe consequences that persist for years and decades after use.”

Saudi Arabia was forced to admit earlier this month that it has used cluster bombs in Yemen, following repeated denials. Ahmed Asiri, a spokesperson for the Saudi-led coalition, stated: “It has become apparent that there was limited use by the coalition of the UK-manufactured BL755 cluster munition in Yemen.”

While the Saudi-led coalition claims it will stop using the BL755, HRW warns that the coalition “left open the possibility it would continue using other types of cluster munitions in Yemen.”

This possibility concerns the organization because the attack was launched by another kind of cluster bomb, described as the “ASTROS II surface-to-surface rockets, each containing up to 65 submunitions, delivered by a truck-mounted multi-barrel rocket launcher. Bahrain and Saudi Arabia have purchased ASTROS cluster munition rockets from Brazil, where they are manufactured by AvibrÃ¡s IndÃºstria Aeroespacial SA.” Amnesty International has identified one previous use of this kind of munition in Saada.

While the U.S. government claimed in May that it will stop exporting cluster bombs to the Saudi coalition, the Obama administration has so far refused global calls for a total arms embargo on the coalition over human rights concerns. Meanwhile, the U.S. has been an active participant in the onslaught, deploying troops and helping the coalition identify bomb targets, conduct surveillance and enforce a naval blockade.

Evidence is mounting that the U.S. has a direct hand in war crimes committed against the Yemeni people. The Yemen Data Project revealed in September that over one-third of all Saudi-led bombings are hitting civilian locations, including schools and hospitals. In one horrific attack that took place in October, the coalition bombed a packed funeral in Sana’a, killing at least 140 people.

Earlier this month, the United Nations Children’s Fund warned that as a result of nearly two years of war, “Yemen’s health system is on the verge of collapse, with less than a third of the population having access to medical care, and more than half of the health facilities are non-functional. In addition, every ten minutes at least one child dies of preventable diseases such as malnutrition, diarrhea, and respiratory tract infections.”