An Apache helicopter of the Idaho Army National Guard crashed about two miles south of Gowen Field and Idaho’s Boise Airport, late Thursday night, killing two pilots aboard. The cause of the crash was not yet clear, reports said, adding that an investigation has been launched.

Col. Tim Marsano, a spokesperson for the Idaho National Guard, said that the crew members who were on the AH-64D Apache helicopter, were conducting a night-training mission, reports said. The chopper crashed at about 7 p.m. on Thursday and firefighters initially responded to the crash, Fire Chief Dennis Doan said, according to Associated Press, or AP, adding that National Guard personnel soon reached the spot and took over from the firefighters.

"The men and women of the Idaho National Guard are united in grief at the loss of two of our brothers in arms, who gave their lives while training to defend our nation," Idaho National Guard Commander, Major General Gary Sayler, said in a statement, according to Reuters, adding: "Today, our thoughts and prayers are with their families."

The helicopter that crashed was one of 16 Apache helicopters belonging to the Idaho Army National Guard at the Gowen Field training base, reports said. The Idaho Army National Guard has a training area about 20 miles south of Gowen Field, but pilots also train in other areas nearby, AP reported.