Addressing an urgent debate in the United Nations Human Rights Council focused on the February 28 strike on an Iranian elementary school in Minab, Abbas Araghchi said "more than 175 students and teachers were slaughtered in cold blood" in a "calculated, phased assault".

The strike, he said in a video address, "was a war crime and a crime against humanity, one that demands unequivocal condemnation by all, and unambiguous accountability for the culprits".

UN rights chief Volker Turk meanwhile said the bombing evoked "visceral horror", insisting upon the need for "justice", in a video address to the council.

Mohaddeseh Falahat, the mother of two children who died in the attack, also spoke to the council by video, calling for the diplomats in Geneva "not to let this tragedy be forgotten".

"No mother is prepared to hear the words: 'Your child is not coming back'," she said, in an emotional address.

- 'Deliberate and intentional' -

The attack happened on February 28, on the day the United States and Israel launched the war with attacks across Iran, with Tehran in turn striking targets in Israel and Gulf nations.

A US Tomahawk cruise missile hit the elementary school due to a targeting mistake, according to the preliminary findings of a US military investigation reported by The New York Times.

The newspaper said the US military was bombing an adjacent Iranian base, of which the school building was formerly a part, and target coordinates were set using outdated data.

US President Donald Trump intially suggested that Iran itself may have been responsible -- despite Iran not having Tomahawk missiles.

UN rights chief Turk stressed that "the onus is on those who carried out the attack to investigate it promptly, impartially, transparently and thoroughly".

"Senior US officials have said the strike is under investigation," he said, calling for its findings to be made public.

Araghchi did not wait for the results of the probe to attribute blame.

"At a time when the American-Israeli aggressors, in their own assertions, possess the most advanced technologies, and the highest-precision military and data systems, no one can believe that the attack on the school was anything other than deliberate and intentional," he told the council.

- 'Atrocity' -

"This atrocity cannot be justified, cannot be concealed, and must not be met with silence and indifference," the minister said.

"The United States' contradictory remarks aimed at justifying their crime could not, in any manner, elude their responsibility," he insisted.

Friday's discussion, at the request of Iran, China and Cuba, marked the second urgent debate before the rights council this week, focused on the war in the Middle East.

On Wednesday, a debate requested by Bahrain on behalf of the Gulf Cooperation Council and Jordan, considered Iran's strikes on countries across the Gulf region and their impact on civilians.

Following that debate, the 47-member council approved by consensus a resolution condemning Iran's "egregious attacks" on its Gulf neighbours, calling for swift "reparation" to all victims of its strikes.

No draft resolution was discussed during Friday's debate.