At least 17 Spanish troops with the NATO-led peacekeeping mission in Afghanistan have been killed in a helicopter crash.Up to five other soldiers were injured when a second helicopter made an emergency landing after seeing the first crash. The incident took place during an exercise near the airport of the western city of Herat, according to Spanish military authorities. In Madrid, Spanish Defence Minister Jose Bono refused to rule anything out as to what caused the chopper to come down. He said the site where the helicopter was trying to land “was clear and the procedure should have been uncomplicated.” “There are no known hostile forces in the area,” he added, “but the possibility of an attack has not been ruled out.” It is the second air disaster for Spanish troops involved in Afghanistan. In 2003, a plane bringing 62 Spanish peacekeepers back home crashed in Turkey, killing all those on board.