US military investigators believe it is likely that US forces were responsible for an apparent strike on an Iranian girls' school that killed scores of children on Saturday but have not yet reached a final conclusion or completed their investigation, two US officials told Reuters, the latter reports. Reuters was unable to determine more details about the investigation, including what evidence contributed to the tentative assessment, what type of munition was used, who was responsible or why the US might have struck the school.

US War Secretary Pete Hegseth on Wednesday acknowledged the US military was investigating the incident. The officials, who spoke on condition of anonymity to discuss sensitive military matters, did not rule out the possibility that new evidence could emerge that absolves the US of responsibility and points to another responsible party in the incident.

The girls' school in Minab, in southern Iran, was hit on Saturday during the first day of US and Israeli attacks on the country. Iran's ambassador to the U.N. in Geneva, Ali Bahreini, said the strike killed 150 students. US Secretary of State Marco Rubio told reporters on Monday that the United States would not deliberately target a school.

"The Department of War would be investigating that if that was our strike, and I would refer your question to them," Rubio said. The U.N. human rights office, without saying who it believed was responsible for the strike on the school, called on Tuesday for an investigation.

Deliberately attacking a school or hospital or any other civilian structure would likely be a war crime under international humanitarian law. If a US role were to be confirmed, the strike would rank among the worst cases of civilian casualties in decades of US conflicts in the Middle East.