A strike on an Iranian girls' school that killed scores of children may be the result of U.S. use of outdated targeting data, two sources familiar with the matter told Reuters on Wednesday, providing new details about what would rank among the worst cases of civilian casualties in decades of U.S. conflicts.

Reuters first reported on Thursday that an ongoing, internal U.S. military investigation showed U.S. forces were likely responsible for the strike on the girls' school in Minab.

Video surfaced that experts say appears to show a U.S. Tomahawk missile striking the area. But exactly how the tragedy unfolded has remained unclear and the Pentagon has declined comment, saying the investigation remains ongoing.

The strike, during the first day of U.S. and Israeli attacks on Iran, killed 150 students, according to Iran's ambassador to the U.N. in Geneva, Ali Bahreini.

According to archived copies of the school's official website, the school is adjacent to a compound operated by ​the Islamic Revolutionary Guard Corps, the military force that reports to Iran's supreme leader.

One of the sources, who spoke on the condition of anonymity, said officials responsible for creating targeting packages appeared to have used out-of-date intelligence. The second source confirmed that out-of-date intelligence appears to have been used.

In response to a request for comment, the Pentagon said that "the incident is under investigation." The possible use of outdated targeting data was first reported by the New York Times earlier on Wednesday.

It is unclear how old data ended up being used for the strike and what, if any other factors, might be responsible for the error.

The investigation is still ongoing and it is not clear when a final conclusion will be reached.

Since Reuters' report on the U.S. likely being responsible for the strike, U.S. President Donald Trump has claimed without evidence that Iran was responsible. But since then, he has said he does not know enough about the strike, that an investigation is ongoing and that he will accept the results of the inquiry.

U.S. Defense Secretary Pete Hegseth and other U.S. officials have stressed that the United States would not deliberately target civilians.

Deliberately attacking a school or hospital or any ​other civilian structure would likely be a war crime under international humanitarian law.

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

-Idrees Ali and Phil Stewart/Reuters