The Close Combat (and Shooting) rules mention several times that they are used against an "enemy miniature". There is an exception for Floor Elements (you can attack those too). There is another exception for Explosive Weapons, but "all normal steps apply until Roll For Damage".
I don't think the rules want you to target friendly miniatures.
The best (worst?) you can do is damage a friendly with an explosive shot as long as you target an enemy or floor element. Or hold a Land Mine kicking contest. Or a sing-along on a Time Bomb in a Deadly Virus with Toxic Gas Capsules. I think the rules allow those too.
Hm.. I think you're right. But considering the amount of ways to kill one of your own if you really wanted to, within the rules, I wonder if it would unbalance anything if you allowed both close combat and shooting to target a friendly character. It would be a house rule though.