ABOARD THE USS KEARSARGE — An airstrike that mistakenly killed Iraqi troops on Friday was carried out by an American plane, US officials said on Saturday. Defense Secretary Ashton Carter said he had expressed his condolences to the Iraqi prime minister, Haider al-Abadi.
Carter did not offer a detailed explanation for the errant airstrike, which the Iraqi government said killed at least nine Iraqi soldiers, but said, "It seemed to be a mistake that involved both sides."
"These kind of things can happen when you are fighting side by side as we are," Carter told reporters aboard the Kearsarge, an amphibious assault ship deployed in the Persian Gulf, "on a dynamic battlefield."
Another US official, who asked for anonymity to discuss an episode under investigation, said the plane that carried out the attack was a B-1B bomber, which dropped several bombs as it was supporting Iraqi forces battling Islamic State fighters near Fallujah. At least one of those bombs, it appears, struck the Iraqi troops.
Yet a third US official said that bad weather might have been a contributing factor, and that the Iraqi troops appeared to have been closer to the target area than the Americans understood. According to an account by Iraqi military officials, Iraqi forces advanced after the US plane dropped two bombs only to be hit by a third because the Americans did not realize that the troops had moved forward.
It is unclear if the episode could have been avoided if the United States had deployed teams of air controllers with the Iraqi forces. The American advisers and trainers who are assisting Iraqi troops work inside the confines of several large bases in Iraq, and do not go into the field to mentor Iraqi soldiers or call in airstrikes.
The United States has invited the Iraqis to participate in a joint investigation into the airstrike.
The broader question, however, is whether the "friendly fire" episode will make it harder for Abadi to accept an expanded role for the United States, which is seeking to speed up the campaign against the Islamic State, also known as ISIS or ISIL.