Three Danish soldiers have been killed and one injured when their vehicle hit an explosive device in southern Afghanistan, the Danish army said Friday. The Army Operational Command said their armored vehicle was driving with other supply vehicles when it hit a roadside bomb or a mine. The soldier who was injured was taken to the Danish Camp Bastion. Denmark has about 700 troops serving in the NATO force in Afghanistan. Most are based in the volatile southern Helmand province. Twenty-one Danish soldiers have been killed in Afghanistan since Denmark joined the US-led coalition in 2002.