internecine

in·ter·ne·cine /ˌɪntərˈnisin, -saɪn, -ˈnɛsin, -ˈnɛsaɪn/ Pronunciation Key - Show Spelled Pronunciation[in-ter-nee-seen, -sahyn, -nes-een, -nes-ahyn]
–adjective

1.	of or pertaining to conflict or struggle within a group: an internecine feud among proxy holders.

2.	mutually destructive.

3.	characterized by great slaughter; deadly.

from dictionary.com