friendly fire

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Discharge of a military weapon that injures or kills a member of one's own armed forces or an ally.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Mil.) Weapons fire{9}, such as artillery or aerial bombardment, from one's own forces; -- used mostly when troops do damage or cause casualties among their own forces.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Weapons fire from allied or friendly forces, as opposed to fire coming from enemy forces or enemy fire.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun fire that injures or kills an ally