An explosion at an Army depot in Pennsylvania left at least four people injured Thursday morning, according to officials and multiple reports. >> Read more trending news Officials at Letterkenny Army Depot confirmed in a series of since-deleted Facebook posts Thursday morning that an explosion was reported at the depot. The incident happened around 7:15 a.m., according to WPMT. Update 10:20 a.m. EDT July 19: Col. Steven Ledbetter, the commander at Letterkenny Army Depot, told WPMT that a small explosion and fire Thursday morning left four people injured. Three people were flown to a Maryland hospital in serious condition, the news station reported. A fourth person was taken to Chambersburg Hospital with unknown injuries, according to WPMT. Original report: Officials with the volunteer Franklin Fire Company said three people were flown from Letterkenny after firefighters responded Thursday morning to an “explosion with burn victims.” The Franklin County Office of Emergency Management also told Fox News three people were flown from the Army depot after the blast. It was not immediately clear what caused the explosion. A spokesman for Letterkenny Army Depot told WHTM-TV that authorities do not believe the blast was the result of a terrorist attack. Employees told the news station that the explosion happened in an area of Building 350 used for painting and that they were “worried about peers who ran out of (the) building screaming (and) on fire.” Established in 1942, the 18,000-acre Letterkenny Army Depot employs more than 3,600 people in Franklin County. Its mission is to “deliver superior maintenance, manufacturing, logistics, life cycle support and service worldwide to the Joint Warfighter and our International partners.” Check back for updates to this developing story.