United States 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.

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 Defense 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.

Reuters could not determine how much longer the investigation would last or what evidence US investigators are seeking before the assessment can be completed.

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 UN in Geneva, Ali Bahreini, said the strike killed 150 students. Reuters could not independently confirm the death toll.

The Pentagon referred questions from Reuters to the US military’s Central Command, whose spokesperson, Captain Timothy Hawkins, said: “It would be inappropriate to comment given the incident is under investigation.”

The White House did not directly comment on the investigation, but press secretary Karoline Leavitt said in a statement to Reuters, “While the Department of War is currently investigating this matter, the Iranian regime targets civilians and children, not the United States of America.”

Asked about the incident during a news briefing on Wednesday, Hegseth said: “We’re investigating that. We, of course, never target civilian targets. But were taking a look and investigating that.”

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.

Israeli and US forces have until now divided their attacks in Iran both geographically and by target type, a senior Israeli official and a source with direct knowledge of the joint planning said. While Israel was striking missile launch sites in western Iran, the US was attacking such targets, as well as naval ones, in the south.

The UN human rights office, without saying who it believed was responsible for the strike on the school, called on Tuesday for an investigation.

“The onus is on the forces that carried out the attack to investigate it,” UN human rights office spokesperson Ravina Shamdasani told a press briefing in Geneva.

Images of the girls’ funeral on Tuesday were shown on Iranian state television. Their small coffins were draped with Iranian flags and passed from a truck across a large crowd towards the grave site.

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.