A Saudi Arabian Blackhawk helicopter crashed during military operations in Yemen on Tuesday killing 12 personnel on board. Saudi sources are stating that the cause of the crash was friendly fire.

The four officers and eight non-commissioned officers were killed while on a mission to try to force out the dominant Houthi group and restore President Abd-Rabu Mansour Hadi to power.

It was the largest loss of life involving Saudi forces since a Saudi-led coalition intervened in Yemen’s war in 2015.

The official Saudi news agency SPA quoted a statement from the Saudi-led coalition as saying the Black Hawk came down in Marib province, east of the Houthi-controlled capital Sanaa.