A series of explosions ripped through an army base in the Colombian city of Medellin on Saturday, killing at least two people and forcing nearby residents to flee. The first of at least six large blasts was apparently triggered by a grenade that detonated inside a weapons arsenal, according to witness accounts cited by local media. Smaller explosions continued in the afternoon. Soldiers from a counter-guerrilla company "were handing in their weapons when a grenade went off for whatever reason," Luis Ferney Berrio, a soldier who was near the arsenal, told RCN radio. "The shock wave forced all to fall to the floor." Army spokesman Maj. Fernando Avila called the explosion an accident and ruled out the possibility of an attack. He said authorities were still investigating the exact cause.