WASHINGTON (AP) — Outdated intelligence likely led to the United States carrying out a deadly missile strike on an elementary school in Iran that killed over 165 people, many of them children, in the opening hours of the conflict, according to a U.S. official and a second person briefed on findings of a preliminary U.S military investigation into the incident.

The bombing of the school and its casualties involving children has become a focal point of the war, and if ultimately confirmed to be at the hands of the U.S., would also stand among the highest civilian casualty events caused by the American military operations in the last two decades.

President Donald Trump initially blamed Iran for the attack, later said he wasn’t certain who was to blame, and then said he would accept the results of the Pentagon’s investigation. The issue took on added urgency on Wednesday after the New York Times first reported that a preliminary investigation found that the U.S. was responsible.