Seven US Marines were killed and several others were wounded in a training accident at the Hawthorne Army Depot in Nevada, dpa cited Marine Corps officials as saying Tuesday. Defence officials quoted by USA Today said initial findings show that the incident occurred when a 60-millimetre mortar exploded in its firing tube instead of flying out. The Marines immediately ordered a moratorium on firing all similar mortars worldwide until an investigation clears the weapons as safe, the newspaper said. The blast took place at about 10 pm Monday (0500 GMT Tuesday) at the base, which is located in a sparsely populated desert region some 225 kilometres south-east of Reno. According to its website, the base is used for storing ammunition and weapon stocks awaiting demilitarization and for providing high desert training facilities to military units. 'We send our prayers and condolences to the families of Marines involved in this tragic incident,' said Major General Raymond C Fox, the commanding general of the 2nd Marine Expeditionary Force. 'We mourn their loss, and it is with heavy hearts we remember their courage and sacrifice.'