friendly fire

:  the firing of weapons from one's own forces or those of an ally especially when resulting in the accidental death or injury of one's own personnel Near the river bordering our camp I find the tents of the four soldiers who were supposedly hit by friendly fire. — Janine Di Giovanni After all, accidental attacks, though tragic, are common in war. In 1967 alone, “friendly fire” killed 5,373 Americans fighting in Vietnam. — Michael Oren