An errant airstrike by the Filipino Air Force that fell on their own troops and killed 11 men while injuring seven others on Thursday was confirmed in a statement by government officials. The incident occurred in a battle to retake the city of Marawi from insurgents from the Islamic State.

Delfin Lorenzana, Defense Secretary for the Philippines military said the deadly accident came about because of the “fog of war” and that a mistake was made.

The incident came during what was the first offensive deployment of fixed-wing aircraft in the nine-day operation, aimed at flushing out the Islamist gunmen who have defied expectations by clinging on through days of ground assaults and helicopter rocket attacks.

“Sometimes in the fog of war a lot of things could happen. Accidents happen, like this,” Defense Secretary Delfin Lorenzana told a news conference.

“It’s very sad to be hitting our own troops,” he added. “There must be a mistake somewhere, either someone directing from the ground, or the pilot.”

The Maute group has been a fierce enemy of a military with superior firepower and greater troop strength.

The government is concerned that the group’s brazen attack and its resilience could strike a chord with the Islamic State leadership in the Middle East and win its endorsement as its Southeast Asian affiliate.

The deaths of the soldiers takes the number of security force members killed to 38, with 19 civilians and 120 rebel fighters killed in the battles in Marawi over the nine days.