The restriction on projectiles intended to cause unnecessary suffering only applies to opponents who adhere to the laws of land warfare -- which insurgents can do, though the current crop of ass hats certainly fail to do.
As such, technically zapping them with the finest maiming technology modern science can dream up (as well as summary executions and other bits of extremity much frowned on these days) is permissible, though the political costs of such are obviously show stoppers.
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