The UN's human rights chief has urged the US to conclude its investigation and publish its findings into a deadly strike on an Iranian primary school that happened on the first day of the war last month.

The bombing evoked a visceral horror, Volker Türk said at an urgent UN Human Rights Council debate, adding that there must be justice for the terrible harm done.

The attack on Shajareh Tayyebeh school consisted of two missile strikes in quick succession that killed at least 168 people, including about 110 children, Iranian officials have said.

US media have reported that American military investigators believe its own forces were likely responsible for hitting the school unintentionally.

US Defence Secretary Pete Hegseth previously said the matter was being investigated.

The strike, if a US role were to be confirmed, would amount to one of its worst single cases of civilian casualties in decades of US conflicts in the Middle East.

Türk emphasized that the images of bombed-out classrooms and grieving parents highlight who pays the highest price for war: civilians with no power in the decisions that led to conflict.

He stated that \u201cthe onus is on those who carried out the attack to investigate it promptly, impartially, transparently and thoroughly\u201d.

Iran's Foreign Minister Abbas Araghchi condemned the bombing as a deliberate and intentional attack by the US, demanding accountability for the atrocity.

Earlier this month, Democrats in the US Senate wrote to Hegseth demanding answers about the strike, questioning the circumstances leading to the deadly attack.

The Pentagon has committed to responding to the inquiries raised by Congress regarding the strike, as well as the verification of the intended target and safety measures in place to prevent civilian casualties.